Everybody has a natural threshold of what your body can maintane naturally. Some guys it's 200lbs LBM, some it's 26o-lbm, etc..it depends on a variety of factors via genetics. This is assuming you have your nutrition/training down. To answer your question, if when you come off you're at a level of LBM that you're body can't hold on to natty, then yes, you will eventually lose the muscle unless you hop right back on anotehr cycle. If you come off and you're still within your body's own natural genetic limit, then you will be able to keep most gains long-term as long as your diet/training are on point.