jim:
the impact probably would have shattered many if not all of the bodies on the plane, alive at the time or dead for several hour
Not so sure about that. Depends upon how the plane hit the water. How many were in seat belts, at that point? Unknown. Was it a spiral down/smash or some form of ditching? Unknown.
On the less dire side, water that deep is pretty cold. Tissue breakdown would be slowed. On the not to nice side, human bodies aren't very well built for the pressure at that depth.
A grim business, no matter what.