I suspect this may be too vague a question for a complete answer, due to aircraft system differences. I have flown aircraft with systems that could be isolated in flight from the flight deck (and, perhaps more importantly, reinstated), and others where a trip downstairs would be required. If the rubber jungle dropped on unwary passengers, most would now be very upset, depite PA announcements. Have you now got an oxy rich environment in the cabin? Did the 7 pax that listened to the brief initiate oxy flow from their masks.... Too many variables I suspect.