Apart for their lawsuit against Google, they're ownership of copyright just means they could choose to relicense future code under a different license, even proprietary if they wanted.

At that point, someone else could attempt a hard fork. Same as what AWS did for Elastic search and MongoDB. The existing release code is still under open source license and so would allow for that. But whoever's attempts that fork, unlike Oracle, would not be allowed to change the license terms beyond what the current open source license allows.

And, someone could also choose to not re-use any code, and re-imement from scratch the spec, like what Google did for Android. That said... the open lawsuit against Google is still deciding of the legalities of that one.