So sorry to hear about this. An injury is never easy to deal with. A "re-injury" just seems cruel. I wish I could offer sage advice, but you are in rare territory with a re-injury and your son seems to have a more than reasonable plan to address it. When my son was injured after his sophomore year all he could think about (besides school) was getting back on the field, and competing again. It was strong motivation. There were a handful of challenges along the way to recovery and competing again, but that is a topic for another day.
Please let me know what you guys decide to do and how he progresses. Best of luck!