That would depend on a lot of variables:
1. The biggest would be this: where are you in terms of your "natural" limit? Lets say you used some AAS when you are an athlete coming back from an injury who needs to get back into condition, if you get up to a size that you could possibly be w/o AAS or at least are not that far above it (lets say it is 225 at a given bodyfat and you are 232; it isn't as hard to maintain as it is to build, also due to muscle memory, etc. your limit w/o AAS might actually go up) it will be easier to keep your gains than say a guy who is 80 pounds of muscle above their natural limit.
2. When does your natural test come back: this is the biggest thing in maintaining gains. If your test levels are where they should be again then you should pretty much be in the clear if you are not too far above your nat. limit and your nutrition and training are sound. I've seen all types of numbers, but if you properly use HCG while on, are not on for an excessively long period (lets say 20 weeks or less), and use estro-recep. antagonists properly afterwards you might be pretty good 6-12 weeks after the last of the AAS clears from your body.
Those are among other factors, but another big one is BF%; it would be difficult to maintain more mass at a very low bodyfat; so if you get to 5% and you aren't willing to put on any fat you will probably lose more (it is easier to function properly at lower BF% while on AAS).