Thank you for sharing your son's story. I'm sincerely happy to hear that he's doing so well. One of my son's close high school friends and teammate was diagnosed with Leukemia during his senior year of high school. He has really been through hell, but he took the mound for Maryland for the first time last spring after missing 3 baseball seasons. I get emotional just thinking about it.
I would imagine this experience has forced your son to mature far beyond his years. My only advice would be to trust his judgement, and to support the path he chooses. If he comes to you for counsel, by all means help him think it through, but try not to let your own biases influence him. He may not want to talk to coaches about what he's been through... or he may really need to talk about it. Just support him and be available when he needs you.
Best wishes for his continuing good health.