Individual dependent. But TRT implies long term androgen use(specifically test cyp). The longer you are on the harder it is to re-establish normal homeostatic balance. So somone on a cycle....may do an 4-16wk cycle. Someone on TRT may be on for YEARS. Big difference.
Ive seen individuals go from abusing steroids for years and years then with a quick PCT have levels of 600+ at 50+ years of age. Then Ive seen people in there 20's that can't get above 200 after 1 cycle. Ive even met individuals who have natural levels in the 100's and they'be never done a cycle, so coming off TRT would leave them back at there normal low levels. There is no rule that applies to everyone, just general phsyiological principles that are worked with. This is why TRT and any hormonal supplementation should ideally be done under the supervision of a healthcare professional.
For the most part the longer you are on the more difficult it is to reactivate the HPT axis. However it isnt impossible, but you will need to do it under the supervision of a savvy endocrinologist probably. There have been quite a number of studies with hypogonadal men (both primary and secondary) that shows reactivation is not impossible.
Like he said, very individual dependent. There is the continued mantra that you cannot rebound, ever. Unfortunately, this is really more or less forum knowledge rather than clinically based evidence.
TRT, like the others have said is supposed to be the absolute last option at correcting existing hormone imbalances. Although many have used it for a temporary solution as well and have rebounded.
Here's a little example for you. Everyone at my station, well, everyone used to be on TRT. 3 of them wanted kids, so they ceased TRT for 2-3 months and used hCG provided by the clinic, rebounded and knocked their wives/girlfriends up. A lot of the dudes when I first started here about 4 years ago were on TRT at 22, 24 and 28. After I bugged the **** out of them to get off they finally listened and after 2, 3, and 4 years of being on TRT they rebounded to previous levels following a clinical PCT with Clomid and hCG. This clinic also utilizes hCG every few months to keep the testes active.
My dad was also on TRT for a year and a half, came off without a PCT and rebounded to higher than pre-TRT levels.
Why am I saying all this? To encourage getting on TRT and getting off? Absolutely not. The point is, a lot of the stories you hear about people never rebounding or getting at least close to pre levels is largely influenced by forum mentality. Most men will rebound. The thing to keep in mind, is how bad will it suck when you're not most men and your dick is broken? Is it worth it? In my opinion, no. Any clinic that isn't a glorified steroid shop is going to keep you around 800 tops, which in the big scheme of things, even if you're at 400 ng/dl isn't going to be worth the lengthy recovery.
The guys here when they ceased TRT had a hard time getting in the gym, one of them slept a lot from lack of energy etc. The thing is, you'll likely rebound but if you go through hell to rebound even with pharmaceuticals to help you what's the point?
The main difference with a short cycle vs TRT is the length of time it will take your body to return to its once pre-TRT state and the increased risk of not getting back to where you once were. You will likely rebound, after a lengthy amount of time of course. During that time there's a good chance you'll lose your gains anyways, so while the advice may be somewhat misguided on saying you'll never rebound, it's with good intent to let you know a very real possibility, albeit a relatively small one.