Facebook (excuse me, bunch of FB employees from the Flow team) says no: https://github.com/facebook/flow/issues/7365#issuecomment-45.... Of course, that's exactly what I'd say if I was in charge of a dying project.
Edit: but, their main codebase is in Flow, and that sounds like a mess to migrate, so I wouldn't be _too_ worried. It might slow down, but I doubt it will become unmaintained anytime before Facebook gets sued out of business :-P