As others have said, I think the ET
pilot was shot or clubbed over the head by the hijackers before the plane impacted. I recall reading that the approach was going relatively well, but when the pilot was incapacitated, the plane banked left and pitched down, causing the left engine to dig into the water and pulling the aircraft sideways. Aerodynamic forces flipped the right wing up and over, causing the fuselage to roll over and break up.
The ideal situation would be to hit the water wings-level, putting both engines into the water at the same time so that they shear off simultaneously. Aircraft with rear-mounted engines would be much more controllable. Hopefully the wings and fuselage can skim over the suface like a skipping rock, the fin maintaining some directional control, and stay relatively intact until the aircraft comes to a stop. Going in without wings level would cause spinning or cartwheeling, making the accident much less survivable (the Comoros 767, UAL 232, etc.). A ditching in rough seas would be nearly impossible, although I have heard pilots say there are specific procedures to line the aircraft up with swell patterns.
People in rafts should be able to survive for at least several hours in normal seas. Titanic survivors who made it to the boats, although many were soaked and exposed to below-freezing air, hung on for about five hours without substantial loss of life after the sinking. The crash itself would probably determine the magnitude of fatalities.
Keynes is dead and we are living in his long run.