Don't continue dealing with the dueling doctors..get a third opinion. If he actually has a tear, there's a chance rehab can overcome it, but reality is that he will probably need surgery. What's puzzling is that he was scheduled for surgery when the two of them couldn't decide if he actually had a tear or not..you don't do exploratory arthroscopic shoulder surgery just for the heck of it on the odd chance that you may find a problem.
My son's experience...he was a RHP throwing 87 as a HS soph. Beginning his Junior season, his velocity suddenly dropped to 80-83. He said he was fine, no problems...continued through his SR season, throwing 83-85. D1 schools that had been watching him backed off, because they thought something was wrong, even though they couldn't put a finger on it, and he signed with a JUCO. All this time he was saying he was ok...reality is he was pitching for one of the better HS teams in the state, he wanted a shot at a state title, and he refused to say his shoulder was killing him...and other than his velocity drop, he did a remarkable job covering it up. Right before reporting to JUCO, he hurt it longtossing, to the point he couldn't even play catch.
His JUCO team sent him to the team Dr., and they spent his Fall and most of his Spring trying to rehab him with therapy. They finally scheduled surgery on him...without doing any kind of imaging, just to look for a problem. I got rather upset, to say the least, cancelled the surgery, and brought him home to a good Sports Med MD. His initial physical exam, the Dr. diagnosed labral tear, and scheduled an MRI. MRI showed significant labral tearing...he had arthroscopic surgery...once they were in fixing the labrum, they found rotater cuff tears that didn't show up on the MRI. That was June 2003. He rehabbed that Summer and Fall, and finally got on the hill Spring 2004 once the weather warmed up. He ran into a lot of problems with shoulder/bicep tendenitis that year and the next. Two seasons of JUCO later, he's now with a D1 team as a redshirt Jr., throwing with no pain, living in the mid to high 80's, touching 90.
He went through a lot of pain with the rehab and the recovery, and a lot of hard work. Players have a very good chance of being better than ever after Tommy John surgery, but there are no guarantees with labral/rotater cuff surgery. The success rate is much lower.
Hope your son turns out ok. Definitely see a reputable third MD before going on a fishing expedition inside his shoulder.