Well I was going to either have them try dieting which makes them shrink back down to their original size and weight but remain as monsters, or have that crash and they grow bigger, fatter and hornier. They will transform further; I had plans for more spikes, tusks, maybe wings. I also planned for their kids to rapidly grow up to adulthood and be a handful to the group.
In the direction where they shrink down, Fury will return and reveal the two scientists accidentally dropped the stone and the science crew get exposed, becoming a horde of monsters the Fantastic Four have to stop. Otherwise if they can't shrink back, they slowly bit by bit start to enjoy and even revel in being big, fat monsters eating rocks and trees and grinding out more kids.
