If Israel is about to be wiped out, I'd assume the former Allied powers would step in (because it'll look
terrible if they allow Holocaust II) - enough to prevent (too much of a) massacre but not enough to save the country. Jews may be allowed to remain in Palestine but 'encouraged' to 'return home' to the west. (That's going to be an ongoing impact on continental Europe) Latin America could be a destination but a lot of Italians and Germans went to Argentina post-war and I bet the Holocaust survivors would really love having to live next to them
What would happen to Arabic Jews is a horrible question - the ones who fled to Israel, what happens to them? Do Arabic Jews still living at home get pressured to leave - and if so, where to? - or does anti-semitism in the Arab world begin to gradually trail off now Israel's gone or do they end up as permanent third-class citizens being used as the "let's all beat THAT guy up" target when a regime wants to bolster itself?
What would be the status of Zionism; would Jews ever attempt to create another homeland anywhere else on the planet, and if they did, would they meet any success?
1948/9 is a time when nobody's going to be creating a homeland of foreign settlers. This is when the empires are in decline and independence movements are on the up (and there's no WW1 - Tom Segev's
One Palestine Complete pointed to Britain hoping American Jews would support them as a big reason for the promised homeland). They're stuffed there.
Maybe Stalin will further open up the
Jewish Autonomous Oblast as a PR move but how many Israeli Jews will want to move to Stalin's USSR?