That's not my reading. From the patent grant:
> Facebook ... grants to each recipient of the Software ... license under any Necessary Claims, to make, have made, use, sell, offer to sell, import, and otherwise transfer the Software.
This doesn't say that they're granting you a license to their patents, just their software. In fact, about patents they go beyond to say:
> ... no license is granted under Facebook’s rights in any patent claims that are infringed by (i) modifications to the Software made by you or any third party or (ii) the Software in combination with any software or other technology.
IMO that's pretty clearly saying you don't actually have any license to their patents. Regarding the termination clause:
> The license granted hereunder will terminate....
It seems pretty clear the only license granted hereunder is the one to use the software; in other words if you sue FB for patent infringement you lose the right to use React/Reason.