I got to the last floor, traded blows with the Lich King a few times... and then he warped behind a bunch of other mobs. I lured those mobs away, killed them, and cleared out the rest of the floor, but never saw the Lich King again, even after going around the whole floor again three more times. Is it supposed to be possible for him to escape and render the game unwinnable? (Might he have stepped on spikes while I was dealing with the regular mobs?)