Honestly what would be the best solution imo would be to chose if we want to stay as a guy or stay transformed as a girl
Agreed he can even make it super narrative like our body begins breaking down and we end up in the emergency room at "that place" in a medically induced coma where we wake up in that mindscape realm with our mom again and she tell us that our cells are degenerating because it's becoming too hard transforming between genders so we have to make a permanent choice. Thatd be cool