<not a lawyer>
In particular my reading is that the BSD license alone gives anyone an irrevocable right to use, modify and redistribute the software providing only the conditions in that license are met.
So one can either ignore the PATENTS file altogether or to formally fork the repo while omitting this file and it would be as if that file never existed.
Facebooks' (et al.) claim that these two files together constitute the governing license should be challenged as fraudulent - if they want to relicense react under a new license that contains terms regarding patents they can do so but the last revision before that would still be BSD licensed and the community can fork it.
</still not a lawyer>
So one can either ignore the PATENTS file altogether or to formally fork the repo while omitting this file and it would be as if that file never existed.
Facebooks' (et al.) claim that these two files together constitute the governing license should be challenged as fraudulent - if they want to relicense react under a new license that contains terms regarding patents they can do so but the last revision before that would still be BSD licensed and the community can fork it. </still not a lawyer>