Forgive me if I'm wrong, has been a while since I've been in a G1000 equipped 172 (actually has been a long while since I've been flying any bloody thing!) but doesn't pressing the big red "Display Backup" button take over the map display on the secondary display, incase the primary goes down?
Hence - You can rid yourself of the GPS at the press of a button.
Edit - Ahh, was already mentioned. Missed that post