As I understand it there are a whole shitload of things like cell phone towers that are dependent on GPS timing signals to operate correctly. It seems unlikely that short of full out nuclear war, in which case it kinda wouldn’t matter, the whole GPS constellation would go down. But just how many of those things are necessary to keep stuff more or less running?
From a flying perspective it would be a huge mess... I have flown in GPS denied/jammed environments and everybody gets kinda antsy about that. I bet the airlines would take a huge hit as they would start separating traffic a whole lot more causing big increases in fuel costs. The Russians and Chinese already fuck around with GPS spoofing/jamming and the mil would be up shit creek without it. Off the top of my head only the B-2 and RC-135 use automated celestial navigation. Probably something we need to be looking at adding to a lot more platforms.