I'm not actually air force, but am a bit of an aviation buff with a private license. There would be backup nav systems in manned aircraft, but several popular modern munitions are GPS guided, and I would tend to think that modern battlespace information systems require it as well. Planes wouldn't fall out of the sky, but it would be a significant departure from the ideal state.
Of the munitions? I hear JSOWs and especially JDAMs are popular recently.
As far as BIS info, it's not something I've followed closely, but we're talking things like every plane, tank, and infantryman now (soon?) has gps and information on the location of all friendly forces is automatically shared so you cut down friendly fire.
Apparently caf has more info on milspec GPS than I do, I thought that it required the same main band as civilian, and just used additional military bands to increase precision, but apparently it can function fully independently (not really surprising when you think about it). At least that gives you a little info on some of the troubles of failure of military GPS, as unlikely as that is.
Why shouldn't this break military plane GPS as much as anything else. It will also remove the ability of USAF to GPS target missiles onto US population centres, which they have no need to do anyway. They can still bomb the rest of the world no problem.
Military GPS receivers operate on two carrier frequencies, only one of which is used by most civilian models. (And it's the shared military/civilian frequency which is adjacent to the spectrum in question.)
Using two frequencies makes the military receivers more robust, and also lets them do some clever ionospheric distortion cancellation that you can't do with one channel. (Basically they get the benefits of WAAS without actually needing to receive the WAAS signal.)
That said, neither the FAA or the military are going to tolerate any significant degradation of GPS, domestically or otherwise.
Yeah, I was joking a little. Most aircraft would still work pretty well off of inertial data. However there are quite a few weapons systems that just plain won't work without GPS.
BTW, I'm not a pilot, but I work for a government aerospace contractor, so I have some experience in this.
I thought the most common ones (JDAMs) still had an inertial navigation system cause GPS/INS is used nearly everywhere. It'll probably have horrible accuracy (I guess that depends on how the coordinates sent to the bomb are handled... if it can be calculated as an offset of what the INS thinks it is, then it wouldn't be that bad). But still better then unguided bombs.