Does the concept of existence entail the concept of death? I am asking this because many philosophers have tried to prove the existence of god (Descartes through the Meditations) by saying that he necessarily exists. But as experience has shown, things that exist do not exist forever.
Death is not the opposite of existence. The opposite of existence of is non-existence, and the opposite of death is life. Existence does not necessarily entail life, but life necessarily entails existence. So when philosophers argue for the existence of God, they're not arguing that he is "alive", and thus the notion of death is not applicable.
Death and Life do not necessarily imply existence, unless you can show that existence is inconceivable without life.
Does a rock have life? As we know it, A rock is neither alive nor dead, it just is. It exists as distinct and separate from life as we understand it and therefore this suggests that existence itself is conceptually separate from life and death. Ergo existence cannot imply the concept of death, life, immortality or anything else. This suggests that existence just is.
However, what if our most basic assumptions about life are incorrect? What if life isn't cellular, or based around an ability to directly interact with and/or respond to surroundings? What if the assumption is that molecules and atoms are alive because they can display movement and state change, even if only sub-atomically? If these statements hold true, then does this necessarily invalidate the assumption that existence cannot imply death? Arguably again no if your meaning of death is that something was living and can cease to live.
What about if we change our frame of reference and imply that death isn't the opposite of life, but instead that death is the cessation of something, I.e.: The end of it's existence? If a building is constructed and exists for many years before earthquake destroys the building and turns it into rubble. Is this cessation of the building's existence the death of the building?
If you want to throw God into the mix, then what is your frame of reference? If you believe God exists, than does God exist? If you cease to believe God exists, then does God die, or is it that God never existed in the first place, or is it that God simply ceases to exist? Does existence rely on your ability to observe something existing, or does existence require a belief in existence?
Back to your question, when philosophers attempt to rationalize the existence of a divine entity, they are not questioning existence itself, but the existence of something specific. They are not really arguing if there is life or death or even if God is alive or dead or can live or die, but whether God exists at all. From this point of view, rationalizing the existence of God does not imply that one is attempting to rationalize existence vs death.
Elizabeth - Anything with form has a beginning and an end - a definite boundary. And anything with limits falls off one time or the other. Only the formless is real. Tell me, what is existence and what is death? These are just prattle about the truth which the finite mind has tried to express and has definitely failed to arrive at a conclusion according to Aristotle's logic. To know these, we have to transcend both, from the absolute point of view, nothing really exists the way we see it as Quantum mechanics has so clearly put forth. Everything is the same consciousness existing in different ways. Are waves, foam and bubbles any different from the water they are made of? So, nothing ever dies as the law of conservation of energy implies, it just is different. Know who you are and then, we will see about death and existence.
Interpreting 'death' as the ending of existence, then I think, yes it does. If something exists, it could conceivably no longer exist (this requires existing in time), unless if its nature is such that existence is its essence, in which case not (but even then, we could conceive a possibility of something else which exists and then does not).
If we are in a realm outside of time, then death as above makes no sense. So, interpreting the question then as 'does the concept of existence entail the concept of non-existence', then again, yes it does, since if something exists in that realm, we can still conceive of it not existing, even if in fact it does.