Permanent shrinkage won't happen if you take enough time off the gear between cycles and do proper PCT like mentioned above. After about 3-4 weeks with PCT mine fill back out to original size or damn close. The less time you are on, the faster they come back.
Yes of course they grow back. Everything returns to the way it was before your cycle. Cholesterol, test, LH, FSH, everything. HCG just makes it happen faster.