Someone who is dead cannot be kept “artificially alive”.

Of course they can. Unplug the ventilator, the lungs stop getting oxygen, the heart stops, and one by one all the organs stop and die. But so long as an artificial ventilator -- basically just a pump pushing air in and out of the lungs -- keeps oxygen going to the lungs, the heart will continue to beat without any signals from the brain.

The human body is made up of dozens of complex organs, and billions of cells. Death is not like turning a light switch off. Each organ dies at its own rate, and individual cells might continue living for minutes or hours after the heart has stopped pumping blood. There have been cases of people who have died while hooked up to an ECG, and while brain activity usually stops within seconds or a minute of the heart stopping to beat, in a few cases some parts of the brain might remain active for up to 10 minutes.

But without the brain stem, you're dead. The lungs won't pump oxygen without an artificial ventilator, which means the heart stops, and then whether it takes 5 seconds or fifteen minutes, death is inevitable.