Give back? No. Let them expire like Daredevil or sell back cheaply like Punisher or do a distribution type deal like Hulk are all possibilities.
they will not let them expire. that's just not happening in this age. Comic movies are doing well in hollywood, or are at least perceived to be doing well financially.
FF2 is already scheduled for 2017. They will make a profit on this film. I'm 99% certain of it. Profit just gives them the green light to make more or ask Marvel for more. Marvel won't buy it outright, they don't need it.
This idea of Marvel wanting FF/Spider-man/X-men is just our wishful thinking. Marvel already knows if can put a raccoon, a talking tree and their Han Solo and make $$$. They have Star Wars, they have so much more that they don't need it.
Will they take it back if rights expire, yes! But neither company (Fox/Sony) is going to let that happen anytime soon.
Only last year Fox let Daredevil expire?