We take that chance on 100% of open source projects. Maintainers move on to new projects, or simply don't need something any more. If you want 100% control of your future, you have to make everything bespoke.
In this specific case, I think we'd see the industry move away from React Native before we'd see FB suddenly stop working on it. That is, you're more likely to stop using it than they are to stop releasing it.