I never really have big problems with Sigmund if I'm rolling a fighter type - high health, high damage, but low level mages or sneaky types don't really have the hp or damage output at that point to take him down if you don't want to spend potions or wands you really want to save for later. On the other hand, he's so early on that you'll probably loose your character anyways, so it might be best to just guts on going straight for the kill.
I found one of those super-cursed axes the other day, it was AWESOME. It kills pretty much anything, but doesn't allow you to run away. That wasn't a problem until I met the unique guy with a spear(or something) of banishment. Not being able to run away in the abyss is pretty much a death sentence.