Confirming that the Bluefin 21 UAV has reportedly not yet been launched as of the last press conference for the reason 500N specified (narrowing down the search area with the pinger locator first). Seems to me someone said a 3rd pinger hit would be the trigger for launching the UAV and now they have a 3rd and a 4th so I'd expect to the UAV in the water any time now.
As to the lack of debris, is it possible the plane is mostly intact? They did get 2 separate pinger signals (could one be an echo?). I would think that the vertical entry being talked about as a reason for no debris would smash things up but good, perhaps even destroying the pingers. To my mind a gentle landing with the plane in mostly one piece would explain the lack of debris and the still functioning pingers better than a vertical dive.