nah you dont have to stay on.
simplest way of putting it is everyone has a natural genetic limit.
if you're genetic limit is say 15 stone, then if you are 14st and you use gear and get to 16 stone, then when you come off slowly over time you will drop to 15 stone. if you keep your training and diet up then you will maintain the muscle up to your max potential - in this case 15stone.
does that make sense?
ps. although AAS are not technically addictive, they are in a sort of way. I 100% guarantee you wont just do one cycle, EVERYONE and i do mean EVERYONE says that lol, and then 2 years down the line they are on 3/4 cycles a year!