Praying for you son. I understand the confusion and worries this brings to you as it would me. I have raised 3 children and still have a younger one at home, the only advice I could give you on this is that swimming in chlorine water or the ocean would be better then as if it was a lake or pond.
With him being so young, you could just let the nail fall off naturally, as long as he doesn't snag it on anything until the nail come off. Keep the dead part of the nail cut, if possible and soak it in warm Epsom salt water appx. 10-15 mins then apply the betedine. His nail should come back with or without surgery.
As long as he is healthy, being unconscious for 30 mins. he should do fine.
Not much, hope this information helps. I will keep your son and you in my prayers. Please keep me informed on how it turns out.