There is little doubt that the Apartheid army could have kept the system going for many more years, Umkhonto was just a powder puff movement best at blowing up Wimpy's and killing innocent people. And in SA there would have been no breaking up of the army as in, for example, Libya, Syria, etc.
That said, the NP, and most whites, realised that the cost of continuing this system was too high, and decided to end it.
It was a good decision, just a pity that the ANC governments since 1999 have been really poor and corrupt, and one can just hope that this will change and that someone like Mandela will rise through the ANC ranks - that does appear unlikely though, the party appears to attract and promote these corrupt and incompetent politicians.