Greg,
Don, you still need a current path through the body and that is usually to ground somewhere.
The L/N path would not go through the body in this scenario.
There in no need for a path to ground to get a fatal shock. The two conductors in the isolated water set up a voltage gradient in the water. There will be current flowing in the water. The wet person will be a parallel path. It is possible that the parallel path through the person could flow enough current to be fatal. If the water is isolated, a GFCI will not prevent this. Maybe we need to bond the water in the tub as will be required for pools in the 2008 code.
Don
