Yes. One of the first things that happens during a flood of a low-lying town like New Orleans is that coffins float away. And I wouldn't be surprised if cheap coffins fall apart and the bodies float separately.
Quite possible. When the Flint River flooded here in GA a couple of years ago, one of the more serious problems they encountered was LOTS of coffins popping up out of the ground and floating away on the floodwater. They would run into stuff and be broken open, and then the bodies would be floating around loose.
Friend of mine from Albany (ground zero of the flood) said that all the public works people were permanently grossed out because they kept encountering bodies and parts of bodies all over the place. Some were so traumatized that they wound up going on disability.
So yeah, the bodies could be of folks who were already dead. Let's hope so.