I did - by the time I had GRS, three years on HRT, the pathology report said my testicles were totally nonfunctional. (Of course, the adrenal glands produce small amounts of both types of hormones, but it's usually not enough to rely on to prevent ill effects.) However, the general wisdom is that you can't *assume* HRT will eventually shut down native hormone production permanently; the only thing guaranteed to do that is, of course, removing the hormone-producing organs.
So if you wanted to go off of estrogen, you'd probably need to have your T levels checked after a while without HRT (months?) to see if your native production had bounced back or not.