[Porsche-O-Phile]

A couple of rounds would have torn open the fuselage and depressurized the cabin - lots of noise, "fog", etc. and loss of consciousness by all within seconds. TUC at altitude is under 15 seconds. Would have been scary for those seconds but after that, likely nobody remembers anything. Also unlikely the terrorists can don a mask properly in time and also fall asleep, plane continues on autopilot (if enabled, unlikely) or augers in a few moments later.