When a helicopter crashes into water at non lethal speeds, it should roll over and start to sink. The players aboard the vehicle then have a chance to get out or they drown. A high speed or very lethal crash should still kill you though. If the chopper is enclosed, you have to wait for it to fill with water until you can escape. If you do not have diving equipment, the longer you wait to escape would work like trying to stay underwater when you have no diving gear.
When you crash or land on water currently the heli sinks and kills you with no chance of escape and does not roll over first like a real helicopter would. Sunken helicopter also should not get the exploded wreck model.
Water is like quicksand for helicopters unfortunately as the beta. :(