i tried that several times.... dont panic you are not lost until the pump in the room is submerged and fail. ;-)
( ofcourse it depend on the situation, if you cannot seal the leaks and get the water out in other part of the sub then it might be to heavy to reach the surface. Also if the sub is to deep that also be a problem since it cannot push out the water fast enough ).
ANyway good image of a bad situation. ;-)