Muscle is very hard to lose. People grossly underestimate how good our body is at holding onto muscle. Unless you are in a caloric deficit you should not face this issue.

After a cycle, of course you can expect to lose a little bit of muscle because you're test levels are coming back to reality but I would say you can keep at least 8 of your 10-12 lbs that you would have gained on cycle. Any more weight that you gained would be water or due to increased glycogen retention. If you train hard and eat enough food you should be able to maintain a good chunk of your cycle gains.