If one has the habit of marking his position on the paper chart every half hour or hour on a regular basis, one will not get any nasty surprises. Period.
I am navigating using my plotters but the paper charts are always at hand, on a long distance trip, marked at least hourly. I am talking about navigation, far away from land. In sight of land, one is n o t navigating!
If someone flicks the main switch of the GPS satellites or something like, lots of people trusting the system will be sadly surprised or worst.
The world's political situation is such, Arabic wars, Isil, Russian revival, Chinas rocket island and to boot, that idiot donald duck trump! , that we could lose our entitlement the GPS, sooner than later, imo.
l bloody well hope l am wrong!