We know what happens when pilots of 737-200 fall asleep, and neither of them is in position to wake the other up - and neither can the purser.
Since the purser is the only cabin crew member who knows the cockpit door code, any pilots awake (e. g. on oxygen) in cabin is completely helpless till one engine fails and the cockpit door lock loses power - by which time the fuel is nearly exhausted circling above destination, and it is kind of tricky to do a survivable deadstick landing on an unfamiliar plane with just PPL...
How would an A320 handle in that same situation?