I will accept your analysis about the population estimates but even without there being a non-Jewish majority the nature of Israel as a Jewish state would still cease. With a non-Jewish population even approaching 40 or 45%, the pressure to eliminate all distinctions between Jews and non-Jews would be too great. A secular non-ethnic, non-religious state might be the answer but would most Jews in Israel accept it?
Except for the past 63 years, the governance of the Land has changed hands many times, usually remaining anti-Jewish to a greater or lesser degree. I can’t speak for most Jews in Israel, but I’d still be here if it were under the governance of the Ottomans or the British, or even the Mamluks.
Whether or not a particular tract of land belongs to a Jew, we belong to the Land and no other land. Like I said, if the scenario you fear happens, there’s no stopping it. But I’m willing to bet my life (literally) that it will not. On the other hand, if a two-state solution happens, I can see no way it can end other than in total destruction. I’ll bet against a sure thing like that any day. One-state solution is the best option available.