I caaaaan't have it be Dameon. The re-read has reminded me of how much I adore Dameon's character. I was talking to Deb the other day about the prospect of Dameon's death, and (for my own sanity) I'm taking the stance that Dameon won't go the way of all many unrequited-love characters. I'm hoping we will be surprised, and that Dameon will find a way to move on from Elspeth and live on. Regardless of any other signs pointing to him dying, I'd hate to go down the path of because he can't be with Elspeth he dies; it's just not in character or truthful to the series.
That said, there's a dream that Dameon mentions at the end of TKP, that gives weight to the possibility he's going to be the Destroyer. There's some descriptions of heat, smells of sweat and cosmetic oils, then:
I hear the crack of a whip, and I hear Matthew's curses. That's how I know he is there. I hear his voice. I begin to walk towards it, but someone pushes me and I find I am being herded with a group of others down a steep, uneven trail. A whip stings my back, and all at once it is cold and the air becomes damp and thick. I walk on and the others are around me. I feel their fear and then I hear the roaring of some indescribable beast. All at once a man begins screaming...
(p673)
There's tons of other signs still pointing to it being Matthew, but thought this dream was interesting. It's waved off (by Dameon) as being caused by Dragon, but I'm not so sure, it's very similar to the other Entina pit dreams.
This is still just based on the assumption that the Destroyer will be someone that Elspeth knows and loves who is sent into the Entina pit, that she'll then have to try save but stop from gaining access...