I actually disagree. The results would be far bloodier than the current state of affairs, and much less likely to produce the kinds of results leftists are likely to appreciate, but I believe Israel would survive. If Israel needs a major power sponsor and cannot find it in the US or Europe, there's another option: China. Israel has a lot of high-tech weapons development experience, which is exactly what China is looking for, and will pay quite a bit to get. And unlike the US, China is not likely to have any qualms about how their clients behave "internally", or even towards neighbors. Israel will do what it must to survive, but without US backing, what it will have to do will likely be far more ruthless, and if leftists are actually interested in the welfare of Palestinians (rather than just using that cause as a tool for their own purposes), abandoning Israel is frankly the LAST thing they should wish for.