I have never been in this circumstance but, based on many interactions with, and working for, corporates - this is the end of the story. Given that the circumstances cannot be recreated or tested, they are NEVER going to rescind the decision. If you are able to get a medical certificate documenting his condition then you might get somewhere.
Sorry not to be positive but given how rapidly ANY inflight disruption is now publicised on social media - all carriers ere on the safe side. Carrying medical documentation with him may be a safe precaution - even when on trains.