think best case scenario, level flight, only weak wind - flying automatic RTL
then the APM - for some reason reboots.
plane rolls 10deg and pitches 5deg. - blame it on wind or last position of control surfaces.
Is there any chance, it will manage to boot, and get home ? - remember that gyros won't be perfectly still during calibration.
APM leveling data could be saved - would that really make much difference?