Seawater is corrosive and freshly-run rocket engines are hot, with heat speeding up chemical reactions. Dunking the engine in seawater would basically instantly destroy it. The engines are most of what they want to save, so that's a no-go.

It would also have to slow to a near-stop by itself to not be destroyed by the force of hitting the water. Considering that you can do all that with the stuff already on the rocket, seems easier to add some legs and land it than to figure out a way to make it float, survive the seas for a day or 2, and get a ship with a crane tall enough to pick it up and load it.