Sam,Sorry Mike, but the 21st century is here to stay. These days you can use even use a cellphone to get your lat/lon coordinates from the GPS satellites, and then you just have to plot it on a chart. There are some more expensive marine GPS units that also could use the GLONASS system as a backup, which is the Russian version of GPS, in the remote case of the US maintained GPS system failure.
Agreed! And it is not just NAVSTAR and GLONASS satellites anymore. China continues to build its Beidou satellite global positioning system, the European Union has Galileo (which will be fully deployed by the end of the year), and the Indian government is working to expand its IRNSS system.
So, in the next decade, you will have not one, not two, but at least 5 global positioning satellite systems with full coverage of the globe; and as you say, these things are here to stay--unless there is a nuclear war, or some apocalypse level solar activity.
And of course, you're right about GPS system breakdown. A modern smart phone has GPS built in, which works regardless of whether or not you have paid your bill! Combine that with the now ubiquitous portable solar chargers on the market, there is hardly any scenario I can imagine where someone could be stuck at sea and not have access to GPS coordinates--at least not a scenario where they could also take readings from a sextant, then do the calculations they would need.