From what I have read, they became Jewish and assimilated into the general populace.................
They were only ever a small population. They seem to have disappeared during the Assyrian invasions of 700 BC
The modern day "Palestinians" are again a mix of different peoples -- they will have some Judean, north Israelite, Philistine, Hittite, Egyptian, Roman, Persian, Greek, Arab etc. blood.
It's very interesting how nations are formed and die.
One thousand years ago you had a burgundian nation and then poof. five hundred years ago there was no Belarussian nation or indonesian etc.