Forking + rebranding is perfectly viable option. A similar thing happened to the popular Mambo CMS, which had a big community and user base. Over time, everyone switched to Joomla, the rebranded free version - I don't see Mambo mentioned anywhere anymore.

If the same zeal and effort being spent to oppose Oracle were being spent to create a community around a fork, helped by the controversy it'd be a widely known thing already. Couple that with OS vendors choosing the fork over the "mainline", and in a few years the fork would be "the" MySQL, albeit with a different name.