I posted the following elsewhere on A|N at least once if not twice, if I recall correctly. Still, considering the topic of this group, I figured one more time wouldn't hurt anything, and I hope you agree.
Back in the day, before computer programmers started to recognize the liabilities inherent in the hardware, there was a truism to their function: if you were in the middle of writing a report or preparing a spreadsheet or altering a JPEG and the power went out ... what happened? The answer is pretty simple: all your work was LOST. This is because that work was being recorded in what is known as volatile RAM - Random Access Memory - which does not retain the data it holds in the absence of the power the computer needs to operate. Many of us have had that happen to us on our computers, and yeah, it is a royal pain in the neck. Finally, the programmers came up with the auto-save function, where the utility being used automatically stores our progress to the hard drive at intervals, so that if there is a power glitch, most if not all of the work in progress can be recovered.
Our brains are very much like that RAM in that, without power, or in our case, without blood circulating to supply the energy they need, after a very brief time span they lose their capacity to work and with it, the stored knowledge or functionality to operate our bodies. That process is irreversible, even as it is with the computer. Worthy of note, too: There Is No Hard Drive Backup, no ethereal reserve second copy of us, waiting to be resurrected when the body does finally fail.
The theists would have us believe that, regardless of the state of our body, that some soul or spirit or other non-physical entity has US imprinted on it. This entity supposedly has the means to survive the loss and decay of the physical body and goes elsewhere upon death, to some reward or punishment or whatever. The obvious problem is that they can't demonstrate the existence of any of the mechanisms they assert, yet they continue to insist that those mechanisms are out there, along with their god, their heaven and their hell. To me, that whole belief system is a product of their fear of their own death, their inability to face their own mortality. As my man put it:
Man is so built that he cannot imagine his own death. This leads to endless invention of religions.
-- Robert A. Heinlein, Stranger in a Strange Land
I suppose that the skeptic in me should allow for the possibility of some as-yet undiscovered biophysical mechanism that would allow our consciousness to survive the fatal malfunction of the body ... except for the fact that there is not even the least hint of any such mechanism. The heart stops, a given period of time passes, and even if resuscitation is successful, the brain remains damaged beyond repair.
My conclusion is simple: that Homo sapiens is a machine - a truly amazing, self-conscious machine - but a machine nevertheless. The fact is that machines fail, and the uniqueness of each of us precludes that spare parts are not available in all cases to effect repair. Entropy in one form or another wears at all of us; the pieces erode, age and finally break down.
We live, we die, we're gone. I can't see it any other way.