Thus far I've had no problems at all keeping gains post cycle.
First cycle was with Mag-10 for two weeks. I was coming off a loooong cutting phase and was at around 160 lbs. I had been eating around 3500 calories a day for four weeks to get there (went from 158 to 160 in the four weeks prior to the cycle.) After two weeks on Mag-10 I got to 180...I'm guessing those gains were big in part was because I had been cutting for a long time prior to the cycle (despite the fact that I had been eating pretty big - for me - for four weeks prior.) I actually upped my calories for the two weeks post cycle and used only 6-oxo...ended up at 177 and looked much better than I had at 180 (that three pounds had to have been water weight.) I actually continued to get stronger through the two weeks of 6-oxo.
I immediately after used M1T for three weeks (started getting real bad nosebleeds on the 20th day so I stopped after three weeks.) I was at 192. This time I used tamoxifen from Lion and PaCT from BSL (6-oxo and 7-keto.) Again I went higher with my calories...felt like I couldn't eat enough (always hungry.) Ended PCT at 192. Again my strength actually increased a little over the weeks of PCT (and at this point I was solidly into new poundages on the bench, squat and deadlift.)
When I stopped PCT after the M1T cycle I went about two or three weeks without gaining a pound on the scale or the barbell. After that, my strength began to inch up and eight weeks later I was 195.
The third cycle I did was with a 1-test transdermal and MOHN. Over six weeks I got up to 202 lbs. PCT was tamoxifen plus Metacort (by Dermabolics.) At this time I also started using creatine (started with V12, went to Vitargo, and ended up with CEX which I'm currently still using.) I've never been a creatine responder, though, so I'm very doubtfull that this did anything...I was, more than anything, just trying to do everything I could in order to keep what I had gained. I ended three weeks of this PCT at 200 lbs.
Right now I'm 6 weeks after PCT from the third cycle. I was as high (two weeks ago) as 205 lbs. and my strength continues to increase. (I'm not super-strong or anything...305x1 on the bench press and 325x1 on the box squat...but this is brand new territory for me...I've never been this strong.) Right now I'm trying to drop about 10 lbs. of bodyfat before I begin something new (which probably won't be legal.)
Overall I've gained about 40 lbs. in the last six months. I'd say 10 lbs. of that is fat but I'm not gonna complain about that...I went from being skinny to being alot bigger than the average man. I'm not on anything right now (other than food and CEX) and I'm still getting stronger and bigger.
So if you ask me I'd say that, unless you are beyond your genetic potential, you shouldn't have to worry too much about "losing all of your gains post-cycle" unless you are not doing the right things. For me, those "right things" have been: take in at least 1 gram of protein per pound of bodyweight (and use high quality protein sources to do that,) use tamoxifen and 6-oxo together PCT, tighten the diet up a little bit post cycle (eat all clean foods but plenty of...I've been preparing three solid meals each evening for the next day and using a good meal replacement for three more meals,) reduce the frequency and duration of workouts during post-cycle periods (but keep the intensity high) while mixing up the training program every 6-8 weeks, get lots of sleep, no alcohol, and I guess that's about it.
I guess the point is that I think you've got to be able to make progress WITHOUT androgens in order to be able to hold on to gains after a cycle. And to do that you've got to find out what works for you and apply those things consistently.
**disclaimer...I'm an accountant, not a personal trainer or anything like that. I'm not an expert by any stretch.