I've seen it pointed out before though that it would fall back to just the BSD license and others countered saying that was definitely not the case. It seems to be yet another fundamental thing about this that isn't clear or agreed upon at all. Still, your point is important and I hope people read it and consider it.
Also by "license" I meant the "BSD + Patents license" as the Facebook writeup put it.
"...definitely not the case." Citation needed, reasons required, etc. The patent license says nothing about terminating the BSD license. Neither refers to nor affects the other. Without a good legal argument, one must assume that the BSD license applies whether Facebook is being sued over a patent or not.
That answer only addresses the "copyright license", others argue that plain BSD is a "license to use".
If BSD is a "license to use", then it is implicitly a copyright license _and_ a patent licence.
Assuming the above, the argument goes that the implicit patent license in plain BSD is overridden by the explicit patent license in BSD+Patents, and that the explicit one is much more restrictive than the (unwritten) implicit one.
Also by "license" I meant the "BSD + Patents license" as the Facebook writeup put it.