This is an interesting question.

I will try and answer this in perhaps a slightly unorthodox way.

First, let us examine what we know about life. A human being is only 10% human, 90% of the cells are useful bacteria. Being human, then, is not quite what it first appears. Those bacteria handle digestion, program your immune system, even regulate some functions of your brain. Some of those bacteria first appeared long before humans evolved. This raises a few questions as to what a human even is. However, I'll set that aside.

Cells, whether bacteria or human, consist of DNA (a sequence of base 4 instructions that are poorly understood and are likely a lot more complicated than imagined), viruses edited and enslaved by the cell to perform various functions, and chemical messengers. Human cells and some bacteria also have mitochondria, which are also enslaved organisms.

I could continue, but it's not necessary. The upshot is that - at every level - you have a hybrid organism. It's a gestalt, a superorganism of many different creatures, the fact that some have more power than others isn't important. Ok, organism is perhaps not the right word, but how else to describe entities that are confined but exist otherwise independently? They're all borderline on "living", yet unquestionably are alive in their own sense.

We are therefore a superorganism that is comprised of superorganisms. The fact that it's all confined to a frame is of no more importance than it is for the components of a cell. It doesn't change anything of substance.

Now, I'm going to change tack entirely. There have been many cases, now, of patients having their blood replaced with a salt water solution, having their heart stopped, and being cooled to 5'C (about 40'F, I think). They have no brain function. The bioelectrical field has stopped. There is no metabolism. Cells are not using oxygen to gain energy. Is this death?

By any medical standards, it is. There is no detectable indication of any kind of life at any kind of level. There isn't any blood to carry oxygen and therefore all cells have shut down.

This state can be maintained for four hours without harm. It can then be reversed and the patient returns to life. This is now fairly routine in some hospitals for cases where operations would otherwise be too dangerous.

What does this mean? It means pretty much what you might expect it to mean, if you are a superorganism. The cells have adapted to such conditions, so they survive just fine. The patient vanishes when the cells disconnect and reappears when the cells reconnect.

This makes perfect sense, when you think about it. Every cell in your body has been replaced at least once. Including brain cells. Yet "you" have existed throughout all of that.

Are you a computer program? In a way, yes. Everything that happens in you is "computable", that is to say any computer could simulate you, perfectly, if given the same sensory data and enough time to process it.

But you are a computer program in another sense, too. It is a fundamental law of nature that information cannot be created or destroyed. All the information that has ever passed between all the cells that influence you still exists. It was emitted by each cell as electromagnetic radiation. If you replay that information, you would get a person behaving in exactly the same way. Since physics is time-reversible, it is just as legitimate to consider your body as being programmed by that electromagnetic radiation. There is no physical experiment you can perform that can prove which way round it is.

That also means, of course, that death becomes curious. Unless every brain cell and every microorganism in you dies at the same time, whatever is alive at the point of death can't be you. You are simply the product of the imagination of every cell in your body. If half the cells have gone, whatever is being imagined isn't you.

Indeed, since you are a product of the imagination of all the cells, a byproduct of being a superorganism, as shown by the medical procedure described and the DNA research on the microbiome, and since the cells themselves are superorganisms of things that aren't strictly alive, is life itself just a product of the imagination of the non-living? (And does that make us undead?)