It's possible that Soviet intervention would have been less aggressive and maybe not have poured in weapons to promote a communist take over. Gorbachev would maybe have seen risk for the Soviet Union in confronting the west in an area perceived to be strategically inportant.
However, the outcome for SA would have been diferent. Without the demise of the Soviet Union communists would have had a much greater influence on the methods, aims and stratetgies of the 'liberation movement'. SA would not IMO have had such a democratic state and a constitution that promotes human rights.
Eventually would have deteriotated into a one party state with maybe African Socialism similar to Nyerere's Tanzania. Economic decline and political repression would have followed.