I think as long as this remains an internal ANC issue, I don't see there being any immediate problems for SA. But if the MDC are of a different tribe and feel, as they have been, that they are being dominated by another tribe with no chance to decide their own destinies, that is when problems will occur.
Some of the pundits in the West, in reference to the bloodshed in Syria and the Middle East, say that when borders are redrawn, it tends to be in blood. One continent where the borders are as the Europeans drew them, is Africa. If the Africans start to "correct" the mistakes of the past and rejoin broken tribes split between two or more different countries, then the problems will start.
From my distant vantage point, I don't see this on the horizon for SA yet. Lets see what happens.