You really have to determine what you're talking about when you say "palestine" to determine if that entity exists or not. If you're talking about the State of Palestine, as most people are when they say "palestine", then in the minds of around 30% of the world it certainly does not exist:
https://upload.wikimedia.org/wikipedia/commons/0/08/Palestine_recognition_only.svg(and btw, the countries that do not recognize palestine are disproportionately represented among warlight players)
However, barring that, you also have Palestine (hebrew פלשתינה Palestina) as a region, which has been so called for around 2500 years. This region certainly does exist, although it isn't really an entity of any kind:
https://en.wikipedia.org/wiki/Palestine_(region)