Let me begin with several basic facts—more historical than archaeological—on which Joseph Blenkinsopp and I can agree.
When the Babylonians arrived in the Land of Israel, there were no fewer than eight independent kingdoms there and in Transjordan: four kingdoms of the Philistines—Gaza, Ashkelon, Ashdod and Ekron; the Kingdom of Judah; and three kingdoms in Transjordan—Ammon, Moab and Edom. With the Babylonian penetration from 604–582 B.C.E., these all disappeared! There were no more independent kingdoms in the Land of Israel. What happened to them and who was responsible?
The four Philistine kingdoms all had similar relations with Babylon and all shared the same fate: They were destroyed to their foundations, and no amount of clever discourse will save Ashdod from the same fate as Ashkelon (as seen in Lawrence Stager’s excavations) or Ekron (as revealed in Seymour Gitin’s work there). In short, the Philistines were destroyed or exiled; they never returned to the Land of Israel. From that point on, there were no more Philistines! The renewed settlement along the coast, after a hiatus, was done by another, primarily Phoenician, population. Thus, the total change in the population of the southern coast during the Persian period was a result of the Babylonian destruction.