John, I submit that your own mindset as a parent is at least as important as your son's and I encourage you to not only accept where your son lands, but embrace it. As the parent of a college sophomore, I remember all too well the negative emotions I harbored inside my mind as my son faced various challenges during his high school years. The amount of mental energy I expended at times worrying and fretting about his situation was simply incredible. In the end, it all worked out just fine. And I realize now that the struggles and challenges he faced were indeed part of the growing process for him, helping to make him the talented player he is today.
Worst case scenario: your son makes JV or even the freshman team. Worst case scenario: he stumbles mentally and starts playing down. In the end, this may be the best thing for him. It might be much more preferable for him to struggle on a lower-level team than be brought up to varsity and fail magnificently in front of all those competitive seniors and parents and fans and coaches. That alone could deal a strong and lasting blow to his confidence, whereas his freshman or JV teammates and coaches will likely not be nearly as unforgiving.
None of us know how all this will play out. He may make varsity and do fine, or he may make JV and play well and eventually be moved up, or he may make the freshman team and struggle. But no matter what, keep your chin up and embrace the moment. In the end, you'll be very glad you did.
Please let us know how it turns out. Best wishes!