The Jews already living in the Mandate were pushing for independence. Even without the Holocaust, at some point the mandate must end, Britain leave, and the local Arabs and Jews fight each other.
What the Holocaust did was remove the last objections the international community had to a Jewish homeland since the Palestinian Jews could rightly say that if Israel existed, they would have taken in all of the Jews who tried to leave Germany, but which no one else would take.
If the Holocaust didn't happen, but the Nazis still come to power and treated them before the Wannsee conference, I think it is highly likely internation support for Israel exists. There will still be a lot of sympathy. That sympathy may not be as deep or long lasting, but enough to last to the late 1940s. Only difference is that there are several million more Jews who emigrate there after the war.
I think it becomes a much more open question if the Nazis never come to power or World War II never happens. At best, there may be an Israel, but a much smaller country based around Tel Aviv.