Jim will have considerable clout with Disney once the acquisition is complete, and they officially become on the hook to release the Avatar sequels. Given they will own everything Jim-related except Terminator and T2 (of course, to be fair, they'll only own Fox's share of Titanic while Paramount continues to own the other share), he'll be in a position where everyone would have to listen. He'll also obviously never stop being strident in his approach or give up being willing to fight to the death for his vision. This is especially important, because he won't meekly submit to whatever Alan Horn wants. So if Jim tells them he really wants Disney to revive Blomkamp's film, they'll seriously consider it.
Also, do you foresee Jim also injecting himself to stand up to other decisions Horn has pushed Disney for, like potentially shuttering R-rated projects and pushing they reverse position on James Gunn?