I guess this is closest to a modding Q&A post, although it's arguably a mod idea (but you've covered that in a different post already.)
My only real comment here is--I urge you to think twice about employing Jasper in any sort of serious NPC epilogue. He is, after all, fundamentally a gag character who was introduced to BG2 in order to explicitly break the mechanics of the game in Dungeon-Be-Gone.
I was on the fence about including him in Keto, since (unlike DBG) Keto is meant to be a component of a "legitimate, otherwise canonical" game experience. But he seemed to slot nicely into the bard contest, and since both Jasper and Keto were originally Blue's creations, the rewards seemed to outweigh the risks. That's not so much the case for a new Sarevok epilogue.
Epilogue creation is explained
here, by the way.