I've had rotator cuff surgery on both shoulders. One a complete full thickness tear, requiring drilling and anchoringbthe tendon (supraspinatus, specifically) to the humerus (sp??) bone - the upper arm bone. I, tpo, put it off for 10 or so years before having the surgery done.
I will tell you that the pain post surgery is the worst I've ever experienced. I, too have a high tolerance for pain and it literally took my breath away just sitting in my easy chair.
However, after a short time, I found that as long as I followed the Doc's instructions, I didn't hurt all that much. I went to PT for the first surgery. I rehabbed the second one myself in my home gym. I only did this because I knew what to do from the previous; and the second was less serious, not requiring the passive stretching the therapist did with me on the first one.
This was in 2009. I then fracture dislocated the left shoulder 6 months after that surgery and had to start all over again. This injury included nerve damage. My shoulder muscles literally melted away to nothing. I could see the ends of my bones - literally skin and bones! Again I rehabbed it in my home gym.
After this injury I started doing "dumbbell rows" - without the dumbbell, bexause I was too weak to row even a 5 lb dumbbell. Started from there and worked up slowly. Same with lateral raises: started empty handed. Moved up to bands; eventually dumbbells. Today I dumbbell row 80 lb dumbbells for 10 reps per set. I'm up to 200 or so lbs body weight at 12 or so % fat. And I'm doing sets of 5 with 295 on the bench when training chest. And I do ALL the major shoulder movements when I train shoulders. So, YES, full recovery is ABSOLUTELY possible if you work at it.
As I remember, I had to wear a sling for a LONG TIME. I forget now just how many weeks, but I think it was 12. I had the surgeries done back to back and was out of work for a solid 10 months. Thank God I had temporary disability insurance.
Like Mechanic said, worst thing for a joint is to keep it still. I know when I've waited too long between shoulder workouts when they start to HURT! Ironically, when that happens, a good workout always makes it feel better! I tend to use mainly dumbbells for shoulder work, only occasionally doing barbell military press. This helps recruit the stabilizing muscles and builds overall joint strength and helps with "functional strength".
Also like Mechanic said, I've used peptides to help heal. I've used igf-1 with success. I would not hesitate to use HGH if I thought I needed it or that it would help me with something specific. But if you need surgery, you need surgery. MRI should tell the tale.