I just lost my level 42 Lich Necromancer in one of the Pride (in a huge vault in fact), the one with all those teleporting elemental damaging orcs, it survived surprisingly for a longer time than i thought with no healing and on his last legs since Dreadfell.
The battle that cost the character his last life didn't seemed that hard (i had much harder battles) , but it was one in which my character was focused fire by the enemies basically ignoring my minions and my cursed bunnies.
Then before it was too late as damage was accumulating so much that even my high res were simply worthless ( resistance always feel worthless in this game as even at 70% you still take a lot of damage, probably due to everyone having some kind of res penetration in their damage.
I can't even imagine with less res how much one hit kill the game must be
) i control-teleported in a safe place.
But i noticed i was still taking damage. I gave a look to my character and noticed the "Impending Doom" on him, so basically a game over without any kind of hope at that point (i wish there was a big text popping up when you're hit by Impending Doom so you could teleport away instead of staying and getting more damage, i always fail to notice when i'm hit by that horrible spell).
Conclusion : never again i'll play a Cornac Necromancer with the goal to turn it into a Lich, the bonuses are not worth losing every healing/regen (vampiric gift is not a solution because the sustain eat 250 mana ! and in the East due to how very high health everyone has, you need all the mana you can, 500 mana is eaten in a few turns during those battles, and with 250 less mana, you're going to run into more trouble).
I think if you want an undead Necromancer, better play a Ghoul or Skeleton then, because of their healing ability are actually very good .
Ghoul seems to be the better choice, because it does not have the Skeleton heavy experience penalty (Dreadfell with a Skeleton necromancer is hell, you don't have enough skills/talents points because you're not going to be at a good enough level, unless you grind a lot of Farportal, and probably die while trying to do so) and the Ghoul Retch is very good to heal all your minions while healing yourself, while damaging non-undead.