if you use truncateonly the shrinkfile will not attempt to move any pages around so no fragmentation will be caused in this case.

Therefore this is safe to do and worth a shot as a first attempt to see what you get back. However the chances are you will not get anything back in my experience. I do not know of a query to determine is the last extent is in use.

I would advise doing the shrink in chunks rather than trying to get all the space back in one go.