ETR, as the dad of a pitcher that has been through the non-surgical rehab for a UCL injury as a HS sophomore, then nerve transposition surgery in the fall of his freshman season only to end up having TJ surgery that same December, I can somewhat empathize with you. My son's recovery from the TJ was not the "smooth" path that so many attest to. He is 26 months post surgery. I will tell you there are days he calls me and says, "Dad, my arm is bothering me again." It's just words that crush your heart! Thankfully, I think my son's case is simply soreness that he struggles with differentiating from pain, and his complaint is mainly in his tricep. His velocity did return last season. He struggled with control at times and just felt he had no idea where the ball was going. His fall and early preseason have gone great from a control standpoint. I think he just fears the worse every time something doesn't feel "right". (My words not his) But as a dad, I can tell you I will NEVER feel comfortable again. While I completely realize if professional baseball never materializes he will be okay, I also know that it would be crushing for him on so many levels. Like so many of your sons, that has been his dream since the age of 5. It's one thing to fall short of your dreams due to lack of ability, it's another thing entirely when you KNOW you have the tools, but an injury just will not allow to pursue those dreams.
I can only imagine where your son is mentally. I've seen up close and personal the TJ rehab. It is grueling physically and mentally. Then, to find out the ligament is torn again!! How cruel. I don't have the words, but I can tell you that I am pulling for your kid. If he has his mind made up that he wants to do what it takes to try and pitch again, I would go the surgical route. There is no way I would advise my son to consider non surgical therapy based on your comment that apparently you were told it most likely would not help. Again, this is strictly my opinion, so take that for what it's worth. (not much)
I realize I'm just a stranger on a message board, but I can assure you my heart breaks for your son. Whatever path he choses and wherever this injury leads, just let him know there is at least one person that he will most likely never meet that is one of his biggest cheerleaders. I will put you and your son in my thoughts and prayers. As tough as it is on him, I also know you are struggling as well. It's so difficult to find the words to say to our sons. I'm sorry only goes so far. Then it's so difficult as a father to see a child hurting and know there is nothing you can do to take the pain away.