Wetbehindear
I'm aware that this is an aviation forum, not a medical one, so don't want to go too far off topic.
Agree with what you've written about the limitations of CPR and agree that its main benefit is to keep the patient 'alive' until he can be defibbed. I've been to a few collapses where bystanders claim that CPR alone had revived the patient before our arrival but I'd be pretty certain they'd never arrested in the first place. Probably had to hold them down to do it!
Just bear in mind though, that sometimes defibbing does work and a 'do not resusc' policy will ensure that the arrested patient has no chance at all. I know of somebody who arrested mid sentence, was succesfully defibbed, and carried on talking where they left off with nothing more than 'wtf was that?!'.
I'd have thought that an aircraft with easy access to defibrillation would be one of the more likely places to have a successful outcome.