An internal massive betrayal at the hands of uneasy allies resulting in the sudden violent death of several heroic characters and the downfall of the hero faction would require a whole different situation. Not to forget for said characters having a chance to actualy stay dead which would be difficult to do in cape comics at the best of times, but now they have that neat little copy and paste flesh printer setup which more or less makes any violent death meaningless.
Some villains crushing the party? Now that would be a possibility, likely resulting in the heros having some action poses while beating down said villains. But something truely shocking would require a setup which this title has not really delivered.
Unless it's something really out of left field. Like a mutant who is not Mystique killing the five and setting the tree with all the husks on fire, while everyone is distracted at the gala. Though with X-factor still being a thing for the foreseeable future, such a massive disrupton of the replication process would harm that series too much for it to be a shocking turn at the moment.