Once you achieve your desired goal the effects are permanent. You may loose whatever slight amount of swelling you had been retaining when you stop, if they reduce more than you want them to just keep pumping until they hold the size you're wanting. Some who have achieved their desired size still pump a few minutes a day or once a week just to top them off and make them perkier, but it's not necessary once you reach and maintain your desired size. The only way it may not be permanent is if you should loose a lot of weight after you stop. I know I tried going on a rapid fat loss diet a couple weeks ago, and in the first week I lost 5 lbs, and my breasts seemed to start loosing size, where nowhere else seemed to reduce any. Having worked on my breast growth for over 2 years now I didn't want to give up what I've gained so I quit the diet, besides it was screwing up my body too much. Since quitting the diet I think I've managed to regain what little volume I had lost already.
Hope this helps.