It might be possible for e.g. airliners to use military GPS with anti-spoofing (encrypted GPS signal which is harder to spoof or jam, but which needs special receivers that have to be rekeyed regularly). Obvs that would require some bureaucratic cooperation between the air carriers and the military. Also, at least near airports, ground beacons can be used the same way.
Obviously the stuff with maps and triangulation, or celestial navigation can be done by computer now, instead of by some crewmember with a calculator. But GPS is sure a lot simpler to use.
Spoofing GPS, GLONASS, Galileo, and the Chinese system (I forget what it's called) all at the same time might be much more difficult than spoofing just one.