The military wing of the African National Congress, Umkhonto we Sizwe (MK), was known to be a pretty inept force, incapable of even participating in the Border Wars of the 1970s and 1980s.
It never seriously threatened the Apartheid South African government, and despite a good number of camps and facilities in the frontline states, it never expanded its efforts beyond token bombings.
It is interesting to wonder what would have happened had they tried to invade South Africa at some point in the 1980s and forcefully depose the government. Perhaps they could have had support from SWAPO, Mozambique, Zimbabwe, and the Cubans. Would such an invasion have much chance at success, perhaps in touching off a domestic rebellion to aid their efforts? Would SADF, who would not have access to air support, be able to crush such an invasion using their superior armored car, light infantry, and guerrilla tactics?
Where would the invasion be kicked off from? A broad front, or perhaps a strike directly at what is now known as Limpopo Province, where in OTL, MK found its only border area where they would try to infiltrate with any measure of success.
If such an invasion would see the deaths of major figures like Chris Hani, and perhaps the execution of those held at Robben Island, would this be the death knell of the African Nationalist wing of the anti-apartheid movement, assuming it ends in failure? Would such a move alienate the classical liberal opposition to apartheid as expressed by the Progressive Party and Helen Suzman?