I think this is both how Belkar dies and why he stays dead. He's going to go "**** it" kill the vampire, and be killed in some unfixable way in the process. This will save the world, but the damage to the Dwarven lands is still certain as Durkula is already there.

Roy won't die as he technically has no involvement in these events.

He's evil and has very little care for anything, but he really, really hates vampires, and has shown a reckless disregard for his own life to harm those he hates. (Under the presumption he would just the raised after, see what happened with Miko).