1. The pings tell us that almost without a doubt the plane flew until fuel exhaustion.
2. The only possible way for a ditching to occur with the plane remaining intact is if it was under the control of a pilot. Without flaps the speed would be too high to allow the plane to stay intact.
Getting the plane ditched intact would also require luck, lots of it, in an open ocean ditching. The planning behind this episode appears to be methodical - leaving the final chapter up to luck seems out of place in this episode.
I can't imagine anyone sitting around for 5 to seven hours just to dead stick a plane into ocean swells in the hopes of a repeat of the Hudson river landing, and if a person were to attach importance to trying to keep the plane in one piece, they would want to have the engines running when he or she tried the ditching. So this argues against flying to fuel exhaustion.
I believe the plane broke up and there are floating debris. I also believe that without floating debris, there is no place to even begin a seafloor search.