Just as it seemed that Jon would get the wishing stone back, Sarah completed her wish by saying (I wish) "Jon, could you be a little more like me and Karyn, and stop being so hostile?"
The changes happened almost immediately. The last thing Jon thought before completely becoming the beach bunny Jennifer was Why didn't I keep that stone safe? And then he was gone. He had become just like Sarah and her friend Karyn. As Jennifer, he (or should I say she) would never be able to become male again. Physically or mentally.
Or could she?