I think it looks like this:
1) You are natural - you exercise - you reach your genetic limit after xx years. Then you enter the first cycle, you exceed your natural genetic limit on it, then after stopping you will not maintain anything, you go back to the starting point - of course, you continue training and eat well.
2) You are natural, but you entered the cycle after a year of training - you built a lot of muscle on the cycle, but many of them are still within your "natural" potential - then after stopping you have a chance to keep quite a lot from this cycle. Of course, if you continue training and eat well.
3) As for hgh - the only thing that comes to my mind that is permanent is hyperplasia - this phenomenon does exist - if we multiply our muscle cells, even after stopping, they will be there inside us - shrunken, waiting for us to apply aas with hgh again and they will be able to grow. Except that you can't see them during withdrawal, because they simply shrink, just like all the rest of the cells we already had. The more we get off aas and ignore training and diet, the more they shrink. Our bodies don't like extra, unnecessary muscles.
Also imo it's about the level of hormones that are needed to maintain an "unnatural" amount of muscle - no hormones - no muscles.