I often thought about this even while reading LOTR, but actually seeing Sauron's decline into evil in RoP has me thinking about it even more: could Sauron eventually find redemption?

I believe the answer is yes. In a weird way, I even think it's unavoidable.

Scenario 1: After the destruction of the Ring, Sauron becomes a disembodied wraith...a powerless puff of wind.

For Ages afterwards, he can only drift, helplessly watching the millennia come and go.

Being the perfectionist that he is, he starts examining his life/downfall, obsessively trying to figure out what went wrong.

Slowly, it dawns on him just how far he's strayed from the Light. Slowly, he realizes just how badly Morgoth misled him--and how eagerly he allowed himself to be misled.

Slowly, he begins remembering his true Divine nature...and with it, anger gives way to despair and deep regret.

Eventually, he does the one thing he swore never to do: ask the Valar for forgiveness.

The Valar then debate his fate. I imagine it is a close vote. Maybe the tie-breaking vote goes to Eru Iluvatar himself...

...who decides to have Sauron reincarnated--AS A HUMAN.

(This could mean he walks among us as we speak!)

He then has to live human lifetime after human lifetime, serving others, doing harm to none, being good. Again and again he does this until he finally "gets it right."

Then, and only then, is he admitted back into the pantheon of Divine beings.

Scenario 2: Sauron gets the Ring back. With it, he goes on to subjugate all of Middle Earth, finally bending it all to his will. Reluctant to see a repeat of Beleriand, the Valar choose not to intervene.

He's done it! Finally, all of Middle Earth is in his grasp. Finally, he can remake it into something better, something...PERFECT. No more room for imperfection or imbalance of any kind. Everything will be flawless, exactly as he has intended.

Except...it doesn't happen.

Age after Age, he makes more and more changes, attempting to reshape and remold more and more of the world into something perfect...but perfection remains ever beyond his grasp.

Slowly, painfully, he realizes that all of Arda is Morgoth's Ring...that it is too tainted by Morgoth's evil to ever become perfect...that perfection is therefore impossible.

Now, he is at last confronted with all the evil he has done--and realizes it has all been for naught.

This thought drives him to deep despair. Being a perfectionist who hates failure, he struggles to reconcile his love of perfection with its impossibility. Maybe it takes him a very, very long time.

Eventually...he admits defeat.

What he does here is unclear. Maybe he casts the Ring into Mount Doom, thus saving Arda from himself. Maybe, in his despair, he casts himself in along with the Ring. Maybe he pleads to the Valar for forgiveness, and something similar to Scenario 1 happens.

Conclusion: I guess it comes down to this: if he loves perfection...but perfection is impossible (thanks a lot, Morgoth!)...then, at some point, the tension between the two reaches a breaking point. He then has no choice but to confront his own follies...and I suspect it breaks him on a deep level, finally stripping him of all illusions (such as perfection) and forcing him to confront himself.

Anyway, it's just a thought. I do believe he eventually--a very, very long time after the events of LOTR--finds redemption. But who knows?