Have had a shoulder resection done due to bone cancer - this done in 2002. The deltoid muscle was completely removed, hence I am only able to lift my arm about waist high.
I didn't like the alternative - spread of the cancer to other organs, namely the lungs.
I can still use a shotgun. I added two devices to help lift the gun - a handle behind the trigger guard and a front post on the forend. Your deltoid muscle would still be intact; I did review the procedure on U-Tube (Mayo Clinic). I don't see any cause for alarm, although I would suggest several opinions...
Good luck to you as you navigate through this process.