You're probably right. I guess that, from the beginning, Fox tried to attract Marvel attention and force them to open the negociations (since Fox can't say "Hello Marvel, we know that you want the FF. We don't want it anymore, so we can sell it to you. Oh, yes, if we don't produce the movie in 2015, you will have the right for free, but whatever..." So Marvel has to do "the first step") but Marvel (who knew of the deadline and just gained Daredevil for free) never did this "first step" (and they were right)
I'm pretty sure that this movie is more of a Roger Corman attempt than we thought. The lack of budget, the lack of any kind of promotion... Of course, the very low budget protect them from any big loss (because the movie will bomb and they know it), but I'm more and more sure that it is also for another reason.
I really doubt more and more that they really want to release the thing in theaters. I'm pretty sure that, once the movie is finished, they will use the "Marvel as executive Producer" clause from the contract to "send them a message" (the finished product)
If the movie is as bad, lame and stupid as it seems, then Fox has just to "wait" for a Marvel reaction. I'm sure that Fox will do something like that to force Marvel into negociation "We will diffuse that in theater. Yes, we know, it's bad, and the franchise will be damaged... but we may find an agreement. If you paid us the price of the production (which won't be over 30 or 40 millions $, so that was, for me, the main reason of the low budget. If the budget is too high (100 millions, for exemple), Marvel won't pay and / or, it will diminish the profit) + 200, 300 or 400 millions, we just have to find an agreement)"
So the planned ending, for Fox, is the Corman one (rights bought again by Marvel and movie destroyed and never shown in theater)
I'm not sure that Marvel will do it. Fox has no options, but Marvel have so much options (doing what Fox expect, negociating, in 2020, the right with the rights for starwars film 1, doing nothing and see if Fox will abandon in 7 years or sooner,...)