The scenario you describe is so far from reality that it's hard to take as something other than a creative writing exercise. Israel is not existentially threatened at all. The IDF is far better equipped than all the other countries in the region and Israel was just in the process of normalizing relations with some of its neighbors, including Saudi Arabia. All the military support from the USA isn't saving anyone, it's just funneled there to keep the military industrial complex happy and kill Palestinian children as a byproduct.