What would happen, and what would happen to the ZANU rebels, and would they lose in the long run and there would be a second Bush War by Communists etc?
You need a much bigger white population for that, at least a million, which would require a lot more pre-war immigration. Immigration was basically reserved for middle class Brits with the funds to establish themselves as "gentlemen farmers" or businessmen in the interwar years and the postwar immigration was too small to compensate for that. There were plans of letting Czech peasants and craftsmen settle after the German annexation of Sudetenland and opening South Rhodesia to Jewish refugees, but neither of these schemes were approved.
The most interesting counterfactual is opening up South Rhodesia for Jewish refugees in the 30s, giving it a large enough white population to conquer southern Mozambique with the harbour in Lourenço Marques (Maputo) after the Portuguese withdrew and access to Israeli military aid and Jewish business networks. That might have given Rhodesia a chance. Though it would have required most of the Jews to stay after 1948 rather than move to Israel.
