Kill'em all, 50 years is enough and boot-up Morduverse.
Merged Legion with different memories? How many of us really think we could survive such an ordeal? Cast into a reality where neither I nor any of my friends and colleagues have similar memories let alone consistant with the reality in which we live?
Worse than amnesia.
Kill em all. Giffen Boy too in whatever reality it is that comic book heroes are exactly that, comic book heroes. Have Giffen Boy killed by a karate chop to the throat. A SUPER karate chop.

I think he'd appreciate the irony.