I think Israel should protect the Hashemites when it comes down to it. There's no way one should prefer a (probably militant) Palestinian neighbor on most of the eastern border. Israel flew over the Syrian army when the Syrians tried to come to PLO's aid. What do you think a Palestinian-dominated government in Jordan would look like? A dangerous cocktail of Islamists and Palestinian nationalists most likely. I believe the Hashemites and the Israelis need each other.