Like you say HCG and Clomid help to recover your endogenous test production, so in doing that they avoid that your system have an incorrect hormonal imbalance where cortisol is predominant over testosterone (you dont have testosterone when off gear) and cortisol is catabolic "eating" your newly adquired muscle. If you dont restore your test level as soon as possible, when end your cycle, the escenario before start.
Of course, some muscle may be lost, but if you do a correct post teraphy, almost 50-80% of your muscle will be preserved.