'Few have gained such a victory.'
If (according to the Catholic way of looking at things) salvation is a process and a Road traveled, rather than a one-time event, so is damnation. A person's fundamental choice for or against God doesn't usually happen with a single step one way or the other, although that's not impossible. With very few exceptions, repentance is a process and a direction taken, but at some point the person heading into evil does have to make the freely willed choice to go the other way (the root of the word "repent" means to turn completely around). Even some of the events we consider sudden conversions really aren't: Paul was zealously doing what he believed was the will of God when he was persecuting Christians, so when he discovered what God's will truly was it's not strange that he would immediately go about that work as zealously as he had the first. His fundamental desire to follow God's will hadn't changed.
This brings us to another of the paradoxes we run into when we accept the existence of free will: Can someone ever be far enough along the Road to damnation that they no longer have the ability to change their direction? After all, Catholics talk about saints who've been "confirmed in grace," meaning that they reached a point in their spiritual lives where their wills were so united with God's that turning against Him wasn't an option (it's what will happen to each person who enters heaven - a few just reach the state before then). So, according to human logic, there should be a point of no return when heading into the darkness, just as there is when heading into the light. Manichees and other dualists who see good and evil as being equal in power would probably agree with this idea. Dualism came out of the need for a humanly logical explanation of the "question of evil." Those of us who believe that God's folly is wiser than Men's wisdom might see it differently. Since good (and The Good) is infinitely more powerful than evil, a person is never outside its possible reach. But, as in all things, God reaches out first and the person's free will can either accept or reject the offer, no matter how many times the opportunity arises.
Because we don't have the ability to either fathom the extent of God's mercy or judge the heart of another human being, we can never say that anyone is outside the possibility of salvation. When asked, Tolkien even refused to say whether or not Gollum was saved in the end. He did say that he considered the most tragic event in all of LotR to be Sam's waking and scolding Gollum when the latter seems to be at the point of repentance. Tolkien wrote so much in his letters about Gollum's state of mind, heart, and soul that it's impossible to go into all of it here, but if you look at the subheadings under "Gollum" in the index of the Letters, you'll find some interesting entries to start with. The complexities Tolkien saw in the situation make it even more obvious why no one but God is capable of judging someone. One example, from Letter #181: 'The domination of the Ring was much too strong for the mean soul of Sméagol. But he would have never had to endure it if he had not become a mean sort of thief before it crossed his path.' So, was Gollum responsible for the effect the Ring had on him? I'm certainly not going to try to answer that, and evidently neither was Tolkien.
The phrase "no matter how many times the opportunity arises," calls Saruman to mind. His journey toward evil was a long one, and must have been even more complex than Gollum's, given his identity as the closest thing to an angel in Tolkien's cosmos. Unlike Gollum, Saruman had known Ilúvatar. He'd been sent by the Valar to Middle-earth on a mission. It's possible that he started studying the works of the Enemy in the cause of good. But because he kept the knowledge he gained to himself and began using it for his own purposes, he became (as Treebeard says) 'like windows in a stone wall: windows with shutters inside.' Saruman says of the "last chance" that Galadriel holds out to him, 'If it be truly the last, I am glad,' but the Hound of Heaven pursues him farther - to Bag End, where Wormtongue (rather than Ilúvatar - either directly or through Frodo) ends his chances for repentance. Gríma/Wormtongue himself, it seems to me, is somewhat like Sméagol/Gollum, in that we can't judge how much of his downfall came through his own choices and how much of it came through Saruman's manipulations of his will.
The closest we come in LotR to an example of someone "confirmed in damnation" could be the Mouth of Sauron. He's not an angelic being or a wraith, but a living man who has so united his will with Sauron's that he no longer remembers his own name. Since free will and human identity are so linked in Tolkien's writing, that's a chilling image. It's also the complete opposite of what happens to those who unite their wills with that of God - Who calls us each by name. But if the Mouth of Sauron was still alive when the Ring was destroyed, he would have been a child of Ilúvatar rather than a creature of Sauron, placing him among those who had a choice in how to respond to the loss of Sauron's driving will.
The ability of the wraiths themselves to repent is difficult to know, because they're kept in some state of life by Sauron long after they would normally have died, and they are controlled solely by Sauron's will whether or not they choose to be. Gandalf tells Frodo that if the sliver of the wraith's knife had reached his heart he, too, would have become a wraith completely under the domination of Sauron, even though every moment of being forced to carry out the Dark Lord's will would have been agony for a fundamentally good person. The Nine were trapped by Sauron because they were power-hungry, but whether they actually made a moral decision to hand their wills over to him is a different question. It's even possible that the endless years of being forced to obey him gave them the opportunity to recognize their sins and repent in their hearts, even though they couldn't control their external actions.
I intended this essay to be about repentance, not the lack of it, and I would like to look at a few positive examples. Another Man manipulated by Saruman (partially through Gríma) was Théoden. The movie-makers made an interesting choice in showing him as someone possessed by an evil spirit, but that isn't the way the book plays it. Tolkien's writing shows him much more as someone who's been influenced and manipulated by evil to the point of despair, but not as someone needing to undergo an exorcism in order to make the choice to change his direction. When Gandalf calls him back to hope, he accepts the summons.
The most obvious penitent in LotR is Boromir. His change of direction actually began before the book was published; as originally written, he was an out-and-out traitor. He's one of the characters most affected by Tolkien's decision to allow the book to become more complex, and more adult, than he had originally planned. In the story as it finally evolved, Boromir is one of the best examples of Shippey's statement that in Tolkien's writing "The line between good and evil runs through the human heart." No one is completely evil and no one is perfectly good. Boromir is a basically good person who finds it difficult to accept hope without assurance. He sees no way to assure Gondor's survival other than by using the Ring, and his desire for surety is something the Ring's very nature can twist to its own ends. He falls gradually, but when he hits bottom he quickly realizes his fault and not only repents of trying to take the Ring but gives his life to protect two halflings (not long after he has cursed their entire race).
Galadriel is a study in complexity - one that Tolkien seems to have never completely untangled. At the time he wrote LotR, he saw her as a willful exile who had refused forgiveness (and the chance to return home) when it was offered. In a letter written at the time, he says clearly that she was a "penitent"; her time in Middle-earth had increased her wisdom and allowed her to repent of her rebellion against the Valar. It's after that repentance that she is given another chance to accept forgiveness and return home, through turning down Frodo's offer of the Ring. In the years following the publication of LotR, Tolkien seems to have moved toward seeing her as someone unwillingly caught up in the rebellion rather than one of its instigators. I sometimes wonder if what he learned about her as he wrote LotR led him to think about her differently.
I'm going to end with a life-changing Middle-earth repentance that's one of my favorites because it's so human: Lobelia Sackville-Baggins. She and her husband have been a pain in Bilbo's side since (at least) the ending of The Hobbit, when he comes home to find himself declared dead, his belongings being auctioned off and the S-B's measuring the rooms at Bag End to see where their own furniture will fit. They have to wait almost 80 years to move in because of Bilbo's longevity and because of Tolkien's decision to have Bilbo overrule Shire societal norms by choosing an heir (more on the significance of this in a later essay). All of the S-B's we encounter in LotR (Lobelia, Otho and Lotho) actively work toward increasing their wealth and power. Since this is unusual among hobbits, most Shire residents look on them more negatively than might be true of a family following similar aims in, say, modern American society; note that the land in the South Farthing is acquired secretly. Because Tolkien shows them to readers only through the eyes of hobbits, we tend to look on them negatively, too. Even if they were originally a comic annoyance, by the time LotR was completed they'd become much more - a sobering look at what can happen if someone opens the door to evil by seeking power. Their own ambitions defeat them as an evil too strong for them to control steps through that open door.
Otho had died earlier, still bitter. Lotho dies horribly, killed through the stronger evil he's unwittingly allowed into the Shire. He was, most likely, a prisoner in Bag End for some time before his death, as Frodo suggested. We can hope that he repented during that time, but we'll never know. We do know something of what happens to Lobelia. As is often true when someone has a conversion experience (see the example of Paul, above), the same personal qualities that led her toward evil have the effect, later on, of opening the door to good; Lobelia didn't back down to anyone, and that remained true even when she faced an opponent much too powerful for her. This put her "on the side" of most Shire residents (unlike Ted Sandyman, who effectively collaborated with the enemy). But most hobbits didn't have the courage to stand up to the evil the way Lobelia did, so she became a hero to those who had been suffering in silence - even though she was unaware of that during her time in the Lockholes.
What we don't know about Lobelia's change of heart is whether it began during her captivity. Our first glimpse of her at this point shows us the action of grace reaching out to her - and her response. Frodo offers his arm - and she takes it. The Shire residents cheer for her - and she weeps. She follows her change of heart with actions that show it to be real, especially by leaving most of her wealth to help the hobbits who've been harmed by the troubles that her own family had some part in causing. She also gives us a visible, human reminder of how conversion and repentence always work, even if it's not seen outwardly: grace invites and the person responds. God always acts first.