Good question. I can see two interpretation (but IANAL so am probably very wrong here):

1) BSD license covers copyright, and that patent file covers patent grants. Totally separate things. If you sue Facebook, you retain the BSD license and they can't sue you back for copyright infringement, but they can then come after you asserting you infringed their compression patents and demand royalties.

2) Because PATENTS file says "Additional Grant of Patent Rights Version 2" it could mean an extension of the BSD license. That is the termination would trigger the revocation of copyright license as well not just patent protection.