Dead people come back to life?

When someone dies, he or she cannot "come back from the dead". Well, technically, as far as we know, dead people can't come back to life. But it also depends on what exactly "dead" means. Does it mean your heart has stopped, you have no brain activity, or just simply that your soul has left your body (if you believe in that). I think when people refer to a person as dead, it usually means their heart has stopped, so if someone's heart has stopped then they are clinically dead, right? But I've heard and read about people whose hearts have stopped, been "dead" for a period of time, then "come back to life". So what would that be considered as? I guess they actually didn't "die" since that term has been used it describe something that is gone, never to come back. But I believe that an actual human being is not actual matter, but is a soul, like many religions say. I just think that our minds, emotions, personalities, etc. are too complex to be put into the category of matter, like a chair, or table. On a quantum level, we're all energy. And technically, energy can't be created or destroyed. So when we "die", or should I say our bodies die, I would like to believe that whatever happens the "soul", or the energy that we all are, (since it cannot be destroyed) wherever it goes, there has to be a way that it will resurface again. I believe if there is a  way to go somewhere, there is always a way to get back, even if it is not in the same form, or "body" as before. So can a person come back to life? I don't think "dead" people can just "come back to life" like zombies, but hey, I also don't think there has ever been a human out there that has ever come close to having enough knowledge to confirm anything about death.  Just because we think it never happened, doesn't mean it can't.