Well it's possible that it could've landed, but it probably would've quickly sunk quite quickly after. Imagine if it landed but flipped over a couple of times killing everyone on board and breaking the wings off, then sunk. In that situation I don't think there would be much debris left floating around.
It's just that to me, it seems like unless the plane went straight down like nose-first into the water, it would have slammed around and a bunch of little pieces would have broken off. Don't planes consist of a lot of light-weight materials designed to be light and which would presumably float?