Yes! This isn't legal advice, but, speaking loosely, the license gave you an irrevocable patent license to use React (that's the first sentence). That license only terminated when you brought a claim against Facebook (or a related party; check out the old license [1] for the details) for patent infringement or claimed that one of their patents was invalid.
Two important limitations--the original license terminated if you argued that a Facebook patent was invalid or tried to use patents defensively against them (this has been fixed in the new license, as far as I can tell), and Facebook can still sue you for patent infringement for something other than using React.
You would (probably) only do this defensively against an aggression by Facebook. People don't generally have an interest in alleging patents are invalid, unless they are being sued for infringement of those patents.
Some people do! Check out the top story on HN right now, which is about EFF invalidating a patent held by a patent troll: https://news.ycombinator.com/item?id=9356767. Nobody was suing EFF (admittedly, that's almost a technicality since the patent holder was suing others, but EFF was trying to advance the public interest).
Still, it means that, if Facebook sue you with stupidly-obvious-invalid patent on entirely unrelated product, say a patent that car must have a glass windows, then you can't even defend that such patent is invalid.
Two important limitations--the original license terminated if you argued that a Facebook patent was invalid or tried to use patents defensively against them (this has been fixed in the new license, as far as I can tell), and Facebook can still sue you for patent infringement for something other than using React.
[1] https://github.com/facebook/react-native/blob/6938f4524676e2...