While the medical staff (and family) likely know the severity and prognosis of FDs CO poisoning, and by all means the CPR and ongoing life support indicates a very poor prognosis, it may still be too soon to tell if he could recover (given the limited bit we know- medical staff have clear idea however).
Here is a case where very severe CO exposure and poisoning in an automobile occurred with the patient in a coma, but after 3 days of hyperbaric treatments, the patient came out of the coma on day 7 and after one month was functioning more or less ok.
There are other cases in the literature too, so it seems that while the prognosis is almost certainly dire, from what we know now it may not be futile.
Once Greek family arrives there will likely be more information eventually.
Coma reversal with cerebral dysfunction recovery after repetitive hyperbaric oxygen therapy for severe carbon monoxide poisoning. - PubMed - NCBI