In theory, but that doesn't really matter if that person doesn't exist, you know?

In that case, simply moving to another project is the best option.

Forking someone’s project because they won’t accept your PRs will definitely make them feel harangued by the community. I’m not sure if it necessarily has to be that way, but creating a hostile fork is conventionally considered very rude.

This should change though. That's the correct course of action if a maintainer won't mainline what you want them to. Or is absent altogether.

What makes it hard is that upstream users have no attention bandwidth to dedicate to your project's (meta-project's?) internal disputes. They're just going to decide which fork they think is the main one and use that. If you look at Presto, that's a good example of how hostile forks tend to go; both sides have to insist they're the real project, the main project, because otherwise nobody will use them.

Maybe there's a solution to that other than avoiding forks, but I'm not sure what it would be. It seems like a pretty fundamental challenge.