prosfilaes
Adventurer
What about when you've got 4 HP left and the undead creature rolls a critical on you, knocking you down to -12?
Not dead yet?
I think that's missing my point. If the social contract you're playing under says that characters won't die except in dramatic suicides or heroic sacrifices, then the DM shouldn't put them in situations where that's a problem. Undead aren't completely out of the question--skeletons may be controlled by intelligent creatures or just ignore creatures they knock unconscious, etc.--but ravenous undead like wraiths are certainly something a DM should think carefully about. HP is irrelevant; with this social contract, HP damage simply can't kill PCs.
This is nothing new; 1st level characters in any game don't run into ancient red dragons, with rare exceptions, because it's not in most social contracts for characters to be suddenly annihilated by enemies out of their league, no matter how realistically possible that is. You tailor the fights in a game to what you and the players would enjoy.
Again, I'm not arguing that you should do this, or that this is a normal thing to do with D&D. I'm simply arguing that it can be done, and not only be fun, but be tense and dramatic, that even in a serious game, you can take death off the table and leave important stakes on the table.