im not sure that a whale would stop breathing out of water because it is not capable of doing so - clearly a whale can breath out of water. However a whale will have difficulty breathing out of water because the lungs will be under so much weight and there is no longer a bouyancy force to support that weight. Perhaps under these conditions resperation is so difficult that whale just slowly receives so little oxygen and consumes so much during the strenuous resperation activity that an oxygen debt builds up, the whale passes out, and then simply does not breath anymore and dies. I dont see this as a problem for small whales and certainly not dolphins or porpises but for a large whale, I believe my theory to be viable