That, of course, is called dead reckoning and some GPSes have it, but I wouldn't trust it for very long. [1] I'm not sure what cgriswald is on about. Maybe he just lives in a tunnel or some dead zone, because I've never lost satellite connections. Maybe cellphones can triangulate via cell towers? But how is he getting cell data in his tunnel?
When I lose navigation I just do without. I haven't replaced it with Google or any other cell-based app. The satellite radio often also drops out in these moments despite having a buffer.
Edit: Ah, I see, I meant something sort of other than that read. I've certainly had the experience of not being able to download maps, but mostly on hikes in the middle of nowhere. When I use navigation on foot in the city, hadn't had the problems I have with in-car nav.
[1] Pre-GPS systems used this https://ndrive.com/brief-history-gps-car-navigation/