Most of the GPS units I've used only provide very basic info unless you buy a micro SD card with map data on it and some of that is limited to if you have a subscription with the chip maker. Now, this is for hand held units. In car or dash mount units for vehicles may be different. I believe a lot of them have map updates for life as part of the package but I don't own one, and never really used one to know that for sure.
For cell phones, as long as the GPS app was running with a route already, it will continue to work. I've been told but have not verified that if you disable the cellular connection, the GPS app will still access GPS satellites and allow you to navigate. Since I have handheld GPS units with me when I would be inclined to use a cell phone as a GPS in the wild, I've never tested it. I probably should.