@Ookla the Endless, what if draining someone's health, even slightly, makes them increasingly immune to his other powers? Taking their health would, if you take my suggestion, replace it with cold immunity and an aura that negates Liches abilities: Ice automotons turn to rubble, ice created by Lich melts after coming too close, etc... That would help cancel out his ability to drain them to death, though they would die a few minutes after he stopped if he drained them to that point so their survival would be a toss-up, and he would also be unable to kill them in their weakened state, making it a last ditch escape tactic instead of a finishing move.
I also second Cogs request, though mostly because I'd love to see how you finished up with Chasmfiend. He's a pretty cool character and I'd love to see him continue on.