"By the way the APU can't supply electrical power in flight. "
Actually, some 744's can. There was a modification made to the BCU's which allowed APU generators to come online if ALL 4 engine generators went offline. However, I haven't been able to find out if QF has this type. However, the APU wasn't already running... so it wouldn't have helped anyway. The APU gens probably wouldn't have come online anyway with the BCU's underwater.
Rgds.
NSEU