If something else kills Filk (usually something like a vortex) then the location of the scintillating cave will not be revealed. Very annoying way to lose your ultra. I don't know about wand of destruction... I usually use a wand of fireball if I don't have magic.
I saw in the guidebook thread a suggestion that if you kill him with a slave/pet, it might still count for you. That doesn't sound consistent with my experience with pets, but I guess it might be true.
Hoping to win with every class, doomed. Archer, Barbarian, Bard, Beastfighter, Druid, Elementalist, Farmer, Fighter, Monk, and ULE Priest down.