@BoneyM The Grey Tower is many things, but one of them is the quite possibly completely unprecedented use of Gazul's flames being directed by manling magic, specifically Ulgu. Vampire Souls aren't reachable by Divine magic, as they exist purely in the material world, where Gods can only really reach those in the Warp. The winds of Magic are literally what happens when the Warp has been pulled into the material world, and can affect it. Ulgu is specifically the wind for hidden things and evasion. Can we test to see what happens when some scrub-tier vampire's remains are hit by the Tower, possibly as part of a larger study of "what can we destroy with this mechanism"?
I'm aware you've said in the past that every clever trick to deal with Vampires has been tried and has failed - I only ask because this seems unusual enough that it might not have been tried.
"Well, we sure destroyed the bit of him that was here. Does that just free up his soul to respawn based on the next largest bit of them, wherever that might be in the world? We have no idea."