Temporary gains really aren't gains at all to begin with, they are just a swelling or bloating of the cock from being worked so often, people see and feel this a lot from girth. Actual Penis Enlargement gains, solid measurable gains.......I don't see how you could possibly every lose those, if you force your penis to expand and rebuild it will not have any innate or even the possibility to make itself retract in size.
For example how about those women in Africa who grow their ear lobes to ridiculous lengths. If they take out the ear holding rings, things will retract a tiny bit but their ears will forever be that new size, same goes for the women in I believe eastern asia, who elongate their necks, they can never go back to a normal size or their pre-programmed genetic size. Not gonna happen.