The original reasons don't matter, it will not change.
SA's earning pool is too small to sustain 4 networks.
It definitely is big enough to sustain 4 networks.
The issue with CellC was bad management (CellC), lack of good spectrum (government) and the termination rate fiasco (government).
The lack of good spectrum means that one has to roll out more towers to serve the same number of people, so higher costs, the termination rate also resulted in higher costs, and then roaming was quite expensive (not sure in regards to anymore since Telkom seems to be doing well with it).
In regards to bad management, they are (or were, they might have renegotiatied by now, I didn't keep up with the news) paying a premium on that debt, which escalated the debt problem, causing more liquidity issues, which means they can't invest as much in their network/staff, so worse network performance, and it spirals.
If they had not messed up on how they handled their debt, they would probably be profitable right now.
There's definitely space for 4 players, Rain/iBurst is a good example btw, though they're being bought by Vodacom now. South Africa has a huge geographic area and quite a large population, just have to do something like government's WOAN for all rural at cost price (would probably be better to do something like have MTN and Vodacom combined for it, assign them more spectrum, pay to run it, but now there's no money for that with how government handles everything and the corruption ongoing), and have cities be competition.