Sometimes hospitals will endeavor to be overly optimistic, running a code for way longer than is likely to work. There's a slim chance something pans out, even if the patient is unable to recover from a persistent vegetative stare.

Who knows about his vitals, but he almost certainly didn't significantly suffer, he was unconscious before he could realize what happened.

I saw an accident where a car rolled and a passenger was ejected and his head hit the asphalt at speed, leaving skull and brain matter on the asphalt. The news reported that he was pronounced dead at the hospital about an hour later.

If you saw the video, it was clear that he was hit in the brain stem and was dead instantly from hydrostatic shock. Look at what his arms did instantly.

You're only pronounced dead at the hospital AFAIK (or by a doctor or something), so even when your head just explodes, you have to wait until the ambulance makes it to the hospital to be pronounced dead. Doesn't mean you survived until they decided that chest compressions weren't working.

They also didn't pronounce JFK dead at the scene despite half his brains being in Jackie's lap ...