Directions require more than your satellite coordinates. Map services are frequently polling servers for traffic conditions, new tiles for the map, and so on. You'd hope that these can fall back gracefully but I wouldn't put it past them to not. If you activate airplane mode and disable your phone's cellular connection, even if your phone doesn't disable the GPS receiver, directions may stop working.
Works fine on my Android. I regularly lose cellular reception in the mountains, and it continues to work. Sometimes the tiles are low-res, but still readable. I would expect Apple would design around the same contingency, along with poor cellular service along more remote areas of the Interstate.
Android allows you to pre-save areas for offline use also, not sure if Apple does that. I don't have a mobile data plan on my phone, so if I need navigation, I just save the map area before I get off WiFi.
They do, although in my experience Google Maps is better at this. I actually find Apple Maps to be perfectly usable for everything, but always use Google Maps for directions to the boonies if I'm going hiking or something -- it's much better at caching tiles and keeping them around for directions back once I'm out there as well.
Yes offline maps is nice but the infuriating limitation is that it will save map tiles but not locations or areas that I've saved in "My Maps". One would expect a couple of coordinates to require much less storage than a bunch of map tiles...
