unless you are planning on bodybuilding, when you lose large amounts of weight, you'll lose muscle mass. simply put you at 200lbs need more muscle to haul around all that excess fat than you at 100lbs needs. so in that sense you should have less muscle mass [along with everything else] as you lose.
and muscles are use them or lose them things. it's not just eating more calories than you need [that's how you put on fat]. you actually have to work and maintain the muscles too. there isn't an automatic set amount of muscle everyone has [okay, well there is the basic enough to move your body types of muscles, but you likely didn't lose any of that], it varies based on your lifestyle and habits. so it's one of those variable things. the more active you are [the more you use them], the more muscle you'll keep on you provided you are eating enough.
-google first. ask questions later.