They can't -- not in the confines of this adventure. Destroying the ID Core (and Alfebain, too) means destroying the nine other Maure Scions who exist in one form or another in the unexplored levels of Maure (or elsewhere.)
Get out that copy of Libris Mortis ...
I doubt it will ever come up in the adventure I'm running, but for fun I'm trying to come up with some ideas for those other Maures.
Maurid Worm that Walks Sorceror?
Mithril Golem Inhabited by a Maure spirit?
Elan Epic Psion?
Demilich?
A bigger question, and potentially more problematic, is why the PCs should care if they destroy the Id Core or not. Once Tomorast and Yug-Anark's plots are spoiled — and (crucial) the PCs recover the Scythe, who cares if the evil dead Maures are still around? They really aren't bothering anybody.
