About 95% of ethnic Palestinians, including Jews native to Palestine, can be traced by DNA to three individuals living about 5,000 BC. The roots of the Palestinian people are pretty deep, and they basically derive from the Jewish population of Palestine, who subsequently converted in large numbers to Christianity and then to Islam. As you say, Israelis are a genetic patchwork, for instance including a large number of Eastern European descendants of proselytes. Ashkenazi Jews were a foundational nation of Europe and their activity in converting people of Slavic descent was considerable long before Christianity took root.

There was never any wholesale of expulsion of Jews from Palestine. They are still there, and call themselves al-Filistinayum, a name that was known to the Ancient Greeks.