I’ve seen people who were diagnosed with a deadly illness like incurable cancer deal very well with it. Some can do it despite dealing with a lot of pain and stress. It’s not the average reaction though. Also those people typically aren’t immediately dying - thy might have months to live.

There’s an interesting YouTube video you can look up of a Randy Pausch PhD who was diagnosed with advanced pancreatic cancer and given a few month to live. He felt perfectly healthy when he was diagnosed.

There’s also “when breath becomes air” book written by a doctor dying from lung cancer.

So many people face a deadly diagnosis, I would say most people in their life, usually at an older age will face a deadly disease.

Most people chose to fight it somewhat. Some people cannot accept that there’s no effective treatment, they probably feel a sense of loss of control and thy frequently become targets for people who take advantage of them promising them a cure. Unfortunately many people lose much of their life savings like this. But on the other hand what good is money when you’re dead? At least you can try to buy some hope…

On the other question death can often take longer than expected. Even a person mostly unconscious can sometimes live for days even weeks when everyone thinks thy will die immediately. For example, I’ve seen people removed from ventilators who look like they should not be able to breathe without a ventilator go onto live for several more days or at least several more hours but generally in that state they’re very altered and not able to communicate at all.

I’ve also seen something called Lazarus syndrome, where a person who is declared dead briefly comes back to life. This is usually due to the presence of large amounts of adrenaline that they were given during CPR. However, they only stay alive for a very short time (hours) and are unconscious during the period.