Hang in there Ture and stay positive. Doctors aren't always right...I should know, my wife is one.
As people have been mentioning, maybe high volume or easy runs could still be a possibility in the future. Also, from the times we've chatted when boating together, it seems like you prefer sports that require focus. I would recommend picking up sport climbing as a good substitute for boating and kickboxing. It's relatively safe, but still pretty intense and you have hundreds of routes within twenty miles of your house.
Take care and wish you well on your recovery!