Sounds like you might have missed the Music room where you do meet the Lich -
Look here
http://www.volberding.com/WHints/index.html for some excellent maps. Hopefully that will get you to where you need to be.
If he still doesn't show up (which is extremely unlikely - I've never heard of anyone having this problem but perhaps it is possible) there is a solution. So first let us see if you can find him and if not, I'll tell you what we need to do to save your game!
Wyv