Cryonicists have developed a term called "chronopause" for other purposes which might explain it. They are "ametabolic" or not metabolic during this time and therefore and all functions come to a halt, they do not consider themselves to have died. Since the soul inhabits the body, it is frozen and inactive just as the body and reawakens with it.
If we use the Hameroff-Penrose microtubule theory of quantum consciousness to guide our analysis here, and we assume that the soul resides within these quantum computing and quantum informational aspects of the brain predicted by this theory, then a lack of oxygen and the resultant cessation of energy production in the cells will spell the collapse of these quantum informational state of the brain.
This is because under normal circumstances, large-scale macroscopic quantum states (such as those Hameroff and Penrose propose exist in the brain) tend only to appear at extremely cold temperatures, close to absolute zero. At higher temperatures, the thermal noise of vibrating atoms destroys any macroscopic quantum state. Macroscopic quantum states can normally only exist under the totally placid, thermal noise free conditions.
But according to the Hameroff-Penrose theory, cells use a very clever approach to create macroscopic quantum states in the brain even at the high temperatures (compared to absolute zero) of the body tissues. This approach is called a pumped energy system, whereby you use a constant flow of energy to dampen the thermal noise of vibrating atoms, and in this way, you facilitate a macroscopic quantum state in the brain at body temperature.
This pumped energy system is posited to reside within the interiors of the microtubules in the cells of the body. It allows the interiors of the microtubules to be a calm and placid, analogous to the mirror-like surface of a lake when there is no wind blowing to churn up the water.
However, as soon as the energy supply in the cells is cut off, this pumped energy system fails, and thermal noise then takes over, like throwing thousands of stones into a lake, churning up the water. So as soon as this pumped energy system fails, the macroscopic quantum state existing in the microtubules will collapse, and is destroyed in the brain.
That I would guess would be the moment any quantum informational soul will leave the brain: at the moment of death, when the pumped energy system fails, and the macroscopic quantum state in the brain collapses.
However, there is an information exchange between the macroscopic quantum state inside the hollow cylindrical microtubules, and the molecules in the cylindrical wall of the microtubules (this is how it is proposed that data is exchanged between the quantum state and the rest of the brain; the state of configuration of the molecules in the cylindrical wall of the microtubules encodes information derived from the macroscopic quantum state).
So if a body is reanimated centuries after death, and energy production resumes in the cells, so that the pumped energy system can come online again, and recreate the noise-free conditions inside the hollow microtubules, the macroscopic quantum state could perhaps reboot itself, and resume itself to its lasted "saved" state, using the information stored in the configuration state of the microtubule molecules.
But the other possibility is that once the macroscopic quantum state in a person's brain (which normally exists uninterrupted for the lifetime of the person) is collapsed and destroyed due to death and the cessation of energy production in the cells, then most of the information contained in that quantum state may be lost, and thus it cannot really be rebooted if a body is brought back to life centuries later.
I am not sure what the Hameroff-Penrose microtubule theory predicts itself regarding these two possibilities.
Edited by Hip, 20 January 2017 - 08:18 PM.