One of the most devastating aspects of the Fall of X for Marvel's mutants is that there is so much mystery involved in what happened to the mutants who didn't escape with Emma Frost during the attack on the Hellfire Gala. When the anti-mutant organization, Orchis, attacked the X-Men at their annual celebration, Charles Xavier was forced by Orchis to use his powers to make the vast majority of the 200,000 mutants on Krakoa travel through teleportation gates. They then vanished, with Xavier believing they were all dead (they're not actually dead, just scattered across the Marvel Universe). Now, the mutants who were able to resist Xavier forcing them through the gates (and then escaped with Emma Frost's help) are serving as the X-Men, and part of their new mission is finding out who else survived the new "Mutant Massacre."
Source：https://www.cbr.com/marvel-reveals-fate-x-men-fall-of-x-cyclops-juggernaut/
