Part of it was to be set aside for that. Britain could try to claim "well you didn't explicitly specify how much of it and the new nation just has to respect non-Jewish civil rights", but I don't see it going down too well.
That's true, but that's also why they attempted partition in 1947, and (from what I understand) the "Jewish National Home" meant the creation of a Jewish state. In this case, if Israel does a lot better like in my previous post (#11), the UN may criticize Israel for not allowing them to administer the city of Jerusalem as an international zone but they would also be pushed to recognize Israel's borders as all of Mandate Palestine.
Plus, if Israel does control all of Mandate Palestine, you can rest assure that Ben-Gurion is going to make sure that the Arabs who remained inside Israel (I think it was around 156,000; though there may be more who remain) are going to be protected and not expelled.