If the proposed treatment has any chance of working, I'm not sure it should be written off because of brain damage. Brain damage seems to be difficult to conclusively assess. If there's even a slim chance of improvement, shouldn't he be given that chance?
That is wonderful news about your son puffin. Truly. I expect we all wish that was a possibility on the table here.
Unfortunately, there exists no evidence that there is even a slim chance of improvement, not at present. The US doctor didn't think there was any realistic chance of a cure, and brain damage is not something we are yet able to fix. That makes this case different to that of your son. We all wait to hear about these doctors who've supposedly said there's a 10% chance, but that does contradict every single piece of expert evidence so far.
Also, even if it weren't, and there was a slim chance, it's also necessary to balance that against the presumably much larger chance of keeping someone alive, probably in pain, and with a horribly low quality of life. Charlie's own parents did say they didn't want to keep him alive in the condition he's in, and that was a few months back. He's unlikely to have improved in the interim. So yes there would at least be a balancing act to be done if there were a slim chance of improvement but, depending on how bad a state the person is in already and how slim the chance, no they shouldn't necessarily be 'given that chance'.