As far as pressure differential is concerned, pressurised aircraft are designed so that the pressure is exerted from inside to out & not the other way around i.e. higher pressure inside the cabin.
So if you end up in a position where the pressure becomes greater outside the aircraft than inside, the manufacture (of the type I fly anyway) has negative pressure relief valves installed, that automatically let air into the cabin to equalise the pressure in the event this occurs. There is also a QRH procedure to address this in the event the -/ve presuure relief valves do not work as advertised...