you know what might be a useful way to look at it.

This body is a vehicle, liken it literally to a car.
or better yet, like a computer, the body is the hardware program.

And like a computer, the hardware is designed to encase and give the software a medium through which it can operate.

This is very much like the relationship between the body and the "soul" although frankly i prefer to call it software. I feel that we need to make this knowledge more accessable to the scientifically or logically inclined mind.

The difference is that this body is made of organic substance. Like all things in nature, when an organism is not fullfilling a function in relation to the balance of the ecosystem, it ceases to exist.

Likewise, when this hardware is not running the software program it is designed to house, then the hardware, as per its natural function and state,
will begin to degrade. in a relatively short time, because of this natural decomposition, it quickly becomes unfit to house and store the software program.

they become incompatible. like oil and water they can no longer mix.
there is though, a window in wich, degradation of the body has not reached an advanced enough state to disallow the software to reboot the system.

this would explain your question about individuals appearing dead.
once decomposition has set in, the individual has already decided a priori to move on. (we would hope) when they dont,

you have "ghosts".