Undef, not a stupid question at all!
My implants were partial unders, so both sides' pec muscles were cut to make the pockets.
While I'm currently on no-lift/no-reach orders for about a month, I do expect to get back the muscle tone I had originally. Things just need to heal up first.
Amazingly, even though my implants were HUGE (a major part of my discontent with them - I didn't want HUGE and that doctor didn't listen to me), my gals have already sprung back to their normal pre-surgery selves, and I've had these implants for 5.5 years now.
Even my explant plastic surgeon's impressed, esp since at 54, I'm not exactly a spring chicken. While I know some folks who had a lift along with their implant removal, a number of PSs, mine included, advocate waiting 6 mos to a year after removal to see what the body will do on its own. I have no interest in a lift, even if the body looks awful. But so far, I have to say, things are looking pretty darn amazing under the circumstances.