Yeah, there are pretty much two ways it plays out for the occupants of the plane. If the cabin is intact and capable of holding pressure, it and its occupants get crushed like a pop can; if the cabin is not intact, its occupants get crushed like pop cans. Either way, if you were an occupant of the plane, you most likely had a very bad day.Or the pressure inside equalizes to the outside pressure due to leaks and it stays intact.
Planes are not built to be waterproof, it will depend on how fast it fills up with water.
NPR's Morning Edition had a pretty good segment on this Tuesday morning, and discussed some more technical info. F'rinstance, the aircraft was equipped with several life rafts, and each of them were equipped with beacons that automatically start beaconing when they inflate--and none have. They also noted that the redundancies and locations of the flight systems, combined with the aircraft's fire detection and suppression systems, make it highly unlikely that a fire could've shut down all of the systems as this one's apparently did.
I'll see if I can dig up the URL tomorrow...