So sort of like Jormungand (anime)

There are several fallback options if GPS goes away [1]. Pilots are trained in all of them. Whether or not all the pilots will remember each option is another topic I suppose. For drivers on the ground this was and still is a solved problem using map books. When that fails get out of the vehicle and meet people. I do it all the time.

[1] - https://aviation.stackexchange.com/questions/19295/what-will...