Ah, I had forgotten about Karnak's fast healing. I also wasn't sure if there was a duration. Tyrroth has fast healing 4 in combat where he strikes an opponent and obtains combat focus (best feat out of PHB II in my opinion), but only for 13 rounds. Since he is undamaged, its probably a moot point unless Void brings the heat right away again.
Karnak can borrow Tyrroth's dagger, but he only has the one and its his only weapon: dagger +1, returning. He keeps it around more for flavor than anything else since he relies on fists or ranged spells so its perfectly okay to borrow it. But if you can get a second dagger, you should be set. I don't think Shayuri would want to give up Sigil's fencing dagger, but that is the only other one in the party I guess. If you are totally at a loss for attacks, Tyrroth can polymorph you into a War Troll if we hit an encounter soon, but he will save the spell for himself if we hang out for a bit.