you still have to stitch your applique pieces when using fusable unless it is a wall hanging which will not be washed at all. and if you took a cotton quilt to a dry cleaners for cleaning they would wash it!
as long as you stitch your appliques down they will hold up just fine. fusable is only a tool to hold the peices in place so you can stitch them down. there are some that are permenent bonds that do not need stitching; those are very strong, stiff and about impossible to stitch through...by machine or hand.