People put way too much emphasis on his parallels with Tolkien's Gollum. When you scratch the surface even just a bit, the characters don't have much in common beside being equally enemies to the good guys and the bad guys but one thing that defined Gollum was his addiction.

Gollum was a tragic figure, testing the compassion of both characters and readers. And he got a failed redemption and paid for his last treachery with his life - and he served to show the humanity of Frodo, that even if he lasted that long and longer than most, not even Frodo could resist the Ring in the end, and it was the addiction and greed the Ring generates in beings that proved the undoing of the Ring.

Fain is a completely different character, in nature, in symbolism, in purpose and motivations. Jordan merely gave him a few "Gollum" allusions or perhaps incidental (doubtful) similitudes like having been tortured by the DO. For most of his storyline Fain played a role that had nothing whatsoever to the character of Gollum or the themes surround him. There's no compelling reason, not even just really good ones, to believe Fain's main purpose in the finale will be much like Gollum's.