I just checked the 2004 NCAA documents that impacted "redshirting" at the DIII level. While reading NCAA jargon takes a lawyer, which I am,
one can never be sure if you are reading the rule or exception. But it seems to me that "medical redshirts" on a case by case/hardship basis have been preserved. This will require you and your son to make sure all Xrays and the like are preserved and to get a medical opinion which the School will hopefully support to justify the inability to compete.
Not sure if these stories will help but will give it a try.
When ours was a freshman, the team returned every starter from a 37-11 team but one. On the final practice before the season started, the starting 3rd baseman, team captain and MVP ended up tearing his ACL. He really was tortured because he was also a straight A student. Ended up returning after a medical redshirt to play that 4th year. Admitted it was a huge battle mentally to miss a season for the first time since he was 6. Came back and helped lead the team to an NCAA regional berth coming up one game short of the World Series. Readily admitted that his injury year was the worst ever. Also it allowed him to enjoy an additional season which turned out to be his best ever.
Second story: Ours is currently in Fla getting ready for Spring training. One of his roommates/draft group had a huge 2004 season in the NY/Penn league. By 2005 he had a torn labrum which needed surgery and cost him a baseball season. While rehabbing he was diagnosed with cancer. Saw Brian 2 weeks ago and he is in complete remission. Talked about how he was looking forward to getting to Fla., getting started, and how he will play the game as a "game" and for fun and with a true "love" for what he is doing. No way to explain why this happened.
Two pretty remarkable people. Are there stories remarkable? Not sure. Both readily agreed they are better off mentally and emotionally for the experience of missing a season and cherished the "game" even more when they returned.