With 50 m or more of water over mud. Nope. The plane ail fragment if it hits the water at high speed. Some of these pieces will be small with little momentum. Some won't be very aerodynamic (? hydrodynamic). Can you see a detached aileron flying through this much water and digging itself into the mud.
There are some "out-there" theories present, this is NOT one of them. All you say is absolutely true and provable 100% of the time. I always wonder how people, en masse, can be under such a wrong impression about how matter interacts in our world. This one, for me, needs little investigation. There was a crash of a airliner in the early part of this century that contradicts this physically sound concept. That event did little to reinforce what we should understand about impulse and momentum. On this point then I am willing to give the public a pass, considering ...
The other wild threads that are being pulled though really do deserve to be examined on another forum. IMHO of course.