A musing on the Starboard engine non-detatchment..
Is it possible that the starboard engine was still producing some (more than the port engine at least) amount of power on ditching? This would allow the water, on impact, a slightly less restrained passage through the powerplant and hence it could have experienced insufficient force to shear it off. Could this possibly also explain the aircrafts yaw to port once waterborne.
One things for sure, every piece of torn metal under the wings, the sheared port engine and no doubt buckled underbelly all are evidence of the absorbtion of impact energy which was sufficient to protect the integrity of the fuselage and its precious cargo.
Engineering design, great skill and fortune all played a part in this event. To what degree of each we will find out in the fullness of time.