A: In a word, no! Muscle and fat are two entirely different entities. You can no more convert one into the other than you can change an apple into an orange.
If you let your gym membership lapse, your muscles might shrink, but they wouldn’t turn into fat. However, if you continued to eat the same amount of food as you did when you worked out regularly, your fat cells would begin to plump up. Initially, the scale might not register the change as weight gain, because the gain in fat would be offset by your muscle loss, but that situation wouldn’t last long. Pretty soon, the numbers on the scale would start to creep up, and you’d notice that where you once were toned and defined, you’re now kind of soft.
So it’s not a matter of one body tissue turning into another — it’s more a matter of one type of tissue getting smaller while the other gets larger.