Muscovies do fly, but it's mostly females when they are young. The older females and the males are too heavy to fly high of far. They may fly a little, but not usually to high off the gorund. all though I had one female that insisted on roosting and even though it took alot of effort she would roost up high everynight. then my male got jealouse and he some how managed to get up next to her and roost.
If they are flyers, you can clip one wing and this stops it.
keeperofthehearth ,
I would let the wings grow out, I doubt they will fly or fly far.