Totally agree with Last Third. Even the Sea King leaks when dunked, the advice is to attempt an OEI take-off sooner rather than later. Two reasons, CofG change usually nose heavy, and stab electronics are in the nose so would be soaked pretty quickly. Bearing in mind leakage occurs on serviceable machines an impact like this one had would almost certainly lead to water ingress.
A take-off in this state is a recognised procedure and I doubt if our unfortunate pilot would be able to conjure up an acceptable weight figure whilst sat on the water. He tried an acceptable manoeuvre and it went wrong, for what reason we cannot be sure. I think most of us have been there and been lucky.
Lets not blame a pilot for doing what he is trained to do, lets learn where it went wrong and hopefully be better equipped to deal with that situation if we are ever unfortunate enough to be there.