Jim,
The 3M mask can be sanded off, but of course the area that was covered by the mask will need to be repainted because the paint will be sanded off with the mask. As for how good the coach will look after sanding off the mask and repainting it, that depends strictly on how good the body shop paint department is. If the body shop does very good paint work including the very important prep work, the coach will look as good as a new one, but if they try to cut corners, the quality of the job will reflect it.
I would say that you get what you pay for, but when it comes to paint work that is not always true. Check the body shop and their references out if possible.
Gerald