[Boromir88]

I must say, a wonderful treat to read this, Hookbill.

I promise to have a bit more thought out and constructive points later, but a few random things that came to mind while reading this...

Don't forget Grima and Saruman. Given several chances to repent of their evil ways and each time reject redemption.

I think it mostly revolves around pride, or what Tolkien would label as excessive pride - ofermod. Each of these evil characters can't let go of their pride. Because it takes a remarkable amount of courage and humility in a person, to let go of their pride and accept forgiveness when given. If I recall correctly, Grima does beg forgiveness from Theoden, but when Theoden says "Fine, come back to my side as a worthy counselor and join me in battle against Saruman" Grima runs back to Saruman.

Boromir is a rather different story, because not only does he repay his fall with an act of kindness to defend Merry and Pippin. And not only does it cost him the greatest price one can pay (as you've mentioned), but for the first time, the blustering arrogance Boromir often displayed...he lets go:

"I tried to take the Ring from Frodo," he said. "I am sorry. I have paid"~The Departure of Boromir

Aragorn doesn't demand Boromir reveal his "crimes" and repent. Boromir does this on his own. Admits the crime, admits personal guilt in the crime, and paid for it. I believe redemption is a personal choice, I mean, Frodo nor anyone has to find Boromir "forgiven." However, can't really do much more than what Boromir did. It is an interesting case though, because as you said, even if he is redeemed, he's now dead.

And one final point that I want to throw out here...what about Isildur. He claims the Ring as weregild for the death of Elendil and Anarion. It is, legally, a justified claim, Isildur is taking "payment" for the death of his father and brother at the hands of Sauron. But, it really isn't much different than Gollum claiming the Ring as his because it's his "birthday present," is it? So, what about Isildur's fall, and is he redeemed? Unfinished Tales, The Disaster of Gladden Fields is quite interesting, with regards to the motivations of Isildur leaving Gondor:

When he at last felt free to return to his own realm he was in haste, and e he wished to go first to Imladris, for he had left his wife and youngest son there, and he had moreover urgent need for the counsel of Elrond.

"It needs one greater than I now know myself to be. My pride has fallen. It should go to the Keepers of the Three."

"My pride has fallen," and it sounds like Isildur intended to give up the Ring. Whether he would have done so had he ever gone to Imladris, well, won't be known. However, he was urgently in need of Elrond, and his pride had now fallen. Sort of puts an interesting spin on the whole "ambush" scenario...a sentient Ring knowing going to the "Keepers of the Three" would not be an ideal situation? So, let me draw evil in to kill this guy and get lost in a large river for a while?

Edit: Crossed with Inziladun and it seems like we virtually have the same posts haha.