I would say that the chance of that happening is infinitesimal. If you die of an illness then all the symptoms will be there, your organs will gradually shut down and finally your heart stop beating.
If you die in your sleep your whole body changes. My mother died in her sleep I saw her a few hours later and her whole face and body had changed, there could be no doubt that her life had reached its irrevocable end.
The other thing are that the medical checks for end of life include brain stem monitoring are also fail safe when my sister died after a road accident and we agreed to donate her organs for transplant. She was wired up to a machine and her brain monitored for any sign of activity several times and there was nothing.
These stories of people being buried alive date to a previous age or to cultures where burial followed death, usually within hours and there was not the necessary knowledge or medical intervention that is necessary in any modern country.
Finally you do not want to be buried alive, but you are saying you would be content to be embalmed alive? 
What is our role as older people?
Craig and Lindsay Foreman end their hunger strike in prison in Iran.
Quik question (daughter w new baby)


).
.This has been going on for years. Just think how much pleasure she would have had if she'd gone for it! If we knew when our number was up we could spend accordingly but it doesn't work like that sadly. Just do it and don't think of how long? or when?