I don't know much about helicopters either, but I've heard repeatedly from several sources that DO know much about helicopters that loss of engine power don't mean you loose controll. Obviously, you go down, but you can pretty much control where and how you land the thing. The principle is called autorotation: As the helicopter falls, the movement relatively to the air causes the rotor to spin at great speed, which gives you enough lift to slow the descent to survivable speeds and also gives you limited control over the heli.

Once in the water the heli flips over, yes.

And there are probably a bunch of other things than engine that can go wrong with a heli.