Enforcement of copyrights (and registered trademarks) is at the whim of the owner. It's only common-law trademarks that need to be chased to keep them, as far as I know.
In other words, a business clamps down on derived works where they feel leaving it alone is going to damage their business or on principle, not because they need to do so to maintain legal protection.
(That's why it's always dangerous to rely on "other people got away with it," when using someone else's work. It may be that the owner of a franchise doesn't care what people do with it, or it may be that the owner analyzed the case and chose not to pursue it, and will be offended by your version. Larry Niven is probably a good example: For years, he asserted that everybody was welcome to mess around with his "Known Space" concepts, but then suddenly and loudly changed course, squashing anybody who dared so much as mention the Kzin in a story. It's totally within his rights to make those calls, assuming all his stories are copyrighted properly.)
In the case you suggest, they can license the material--though that probably goes without saying, since they can ask to license whatever they want--but can't "seize" it or argue that they own it any more than the creator can argue full ownership.
