Since everything is simply a result of nature's laws at work, things that we call "alive" are just results of chemical/physical reactions of matter. We have come to use "life" as a term that does nothing more than categorize such things so we can quickly grasp what someone is referring to when speaking of "life".
Proof of the illusion can be found by examining things that tend to fall within the definitions of life (by the way there IS NO universal definition of life) yet are clearly things we don't consider alive. Take fire for example. It grows, consumes oxygen, reproduces, responds to stimuli etc. Yet we don't think of it as alive.
A computer program can be made to grow, reproduce, respond to stimuli, etc. Yet that's not considered alive either.
Since there are such wide varieties of physical and chemical reactions in the universe, we can't make one concept applicable to only some and not others.
"Life" is just a term that early man used to describe himself and other things that showed similar characteristics (eating, sleeping, breathing, etc.) As more things were considered, the definition became harder to pin down. Because nature doesn't care how we categorize it or define it. It just is.
So when these reactions stop taking place, "life" as we know it is over. "Life" after death thus becomes a ridiculous concept. If everything I say, do, and think, requires these physical reactions to be taking place, what is it that could possibly go on "being" once these reactions stop? It would be like saying once a fire is put out, it moves on to a higher plane of existence where it continues to burn. Or, once a tuning fork stops vibrating, it continues vibrating somewhere else.