Professor X was assassinated by biologically engineered assassins in the last issue. It’s established that all mutants who died have “backup memories” that can be implanted into new bodies, effectively resurrecting them from death. However, Professor X was an integral part of that process. And not it seems it’s not an easy fix for Jean Grey, one of the world’s most powerful telepaths, to resurrect Professor X using the same approach.
And I wonder what Magneto plans to do with that sword he fashioned from the broken cerebro that Professor X wore.
From – X-Force Vol. 6 #2