I think air traffic is probably the most resilient group - I’m surprised no one answered! IFR was designed long before GPS and for the most part, GPS has been

I think air traffic is probably the most resilient group - I’m surprised no one answered! IFR was designed long before GPS and for the most part, GPS has been shoehorned into the “old” system. VORs around the country are still “primary” for navigations; airways are still primarily defined around VOR radials; and approach plates to large airports have plenty of non-GPS precision approaches. (Some smaller GA-only airfields that recently got IFR approaches might be WAAS/GPS only). Losing GPS might increase workload for some sectors (en route sectors who won’t be able to clear aircraft direct to waypoints) but not likely TRACON who are vectoring aircraft on pre-defined approach plates. If you pick a random commercial flight on your favourite flight tracker and check it’s route, 99% of the waypoints on it are defined as VOR intersections, not GPS coordinates. (The remaining 1% are likely en-route waypoints and not in the departure/approach area). Also, the instrument proficiency requirements for pilots require multiple approach types to be logged every 6 months so they are definitely capable of non-GPS approaches.