Hi and welcome to HCM.
DNR directive must be approved by patient or his closest familly if patient is unconscious or unaware of his condition. This is evaluated by neurologist
When they put him off vent they try to see is he able to breathe independently. If not, he is put back on the vent immidiately. Every time this is risky maniulation and patient can pass away;he must be put on vent in 20-30 seconds. If he is awake then his condition might improve and there is no reason to force extubation. CPR can always be done, with more or less success. I dont get why compressions depends on his shape.