Use Morbent's Bane to weaken Morbent Fel and defeat him.
<The pieces fit, and the holy artifact is restored, gleaming with sacred light. This should let you defeat Morbent Fel's dark magic.>
<Further down the tunnel, away from the direction you came from, a heinous cackle rings out. It's the clattering laugh of a lich. Morbent Fel is just ahead!>