I'm sure if they do the fallback implementation could just as easily be OpenStreetMap. It's really great to see this open-sourced though. It seems like it would be a common problem.
There is also OSMand that uses OpenStreetMaps and allows you to download tiles for offline access (which is wonderful if you're overseas).
While I realize AirMapView is a library that you can include in your map, I wonder how difficult it would be to modify OSMand to do this, which would be able to leverage the offline maps as well
Not to mention at least in Western Europe OpenStreetMap often has much better maps than any competitor. The routing isn't as good yet but that's getting better quickly.