New mythology will happen. Too many of us nerds are too invested. We will write terabytes of fan fiction, some of which Disney will make into books and recoup. The only way the new movies can completely blow the mythology aspect of Star Wars culture is if they disrespect the Big 3 characters.

As for a mythology in just the movies (as opposed to the new EU), there's still time, and this movie sets up some potentially interesting angles. Like, if Kylo and Rhea are siblings? There's your mythology.