see post on lightning strikes for link to AAIB report on Puma strike and ditching. We worked with Apical to certify emergency floats for AS350 that allow you to take off again after landing on water ( I think it did one full rotation at start up before the TR took over !) . I don't recall too many reports where they have been able to recover the aircraft after ditching , if the sea is dead calm the floats should keep the helicopter floating but how often do you sea a calm sea ?.