Hm, I don't remember anything to that effect. Living Dead doesn't really fit even from a class fantasy standpoint. DRKs are not Death Knights. Death/Undeath is not a theme here.

It's not even that hard to come up with a good invuln concept that isn't overly cumbersome or irritating to the user. For 10 seconds, you cannot go below 1 HP. Any lethal damage that you would have received gets converted to a barrier shield, up to X% of your max HP. When the ability ends, you gain said barrier shield for the next 10 seconds.