Well, I got a lot of experience for killing him. I recieved over 35,000 experience for putting him away, and an additional 42,000 for completing the cursed abbey quest. Plus you recieve 2,000 - 5,000 experience after you defeat each enemy in there, whether it is a Lich or Steel Skeleton, and that tacks on about another 25,000xp, so overall, when I fought him (not counting the quest completion) I recieved about 65K - 80K xp, somewhere in that range.
