The only known planned ditching was the hijacked Egypt air which planned top ditch, and he made a very good attempt at doing so, even with being battered on the head at the time by the hijackers. The aircraft did break up as the wing just clipped the water, but there WERE survivors. Most unsuccessfull 'ditchings' have been crashes, where the aircraft has been out of control eg. explosion, fire, engine failure. If the aircraft is still under control, eg still has hydraulics, power, then there may well be a successful case of a ditching yet.