Assume Fox fails to make a Fantastic Four movie by 2015. As a result of Fox's failure to get a film out in time, the rights revert back to Marvel. What happens next?

Would they try to work them into phase 3 or something? Where/when would they even insert them? Would they skip the origin like Spider-Man and have them be preestablished? I'm pretty sure it'd be harder since they're way more out in the open than Parker.

The only other major character whose rights expired and reverted back to the studio naturally was Daredevil in 2013 iirc, and they just tossed the rights to Netflix since he didn't fit their plans. Obviously they couldn't do that with the FF so would they just shelve them until they found a time/place to use them? They didn't plan for this like they did with Spider-Man and the Sony deal.

The franchise would also probably be in better shape reputation-wise than it was when the Fox merger happened in our timeline since this would be a Fant4stic-less world.

How different would this reboot be from First Steps?
Alternate Timeline: The FF rights revert back to Marvel in 2015. What happens next?