There are two immediate issues:
(i) SA needs oil price of 70+ to break-even fiscally, i.e. to cover all of its government expenditure.
(ii) SA has an exchange rate pegged to the US $
1/
This is not sustainable unless oil price rises sharply soon and then stays there.
But that's unlikely, given a looming global recession and a world moving away from combustion engine.
2/
If SA had a flexible exchange rate, it could devalue Riyal. This would help cut down its imports and make it more attractive for locals and outsiders to invest in the non-oil sector. SA could also have run an independent monetary policy.
3/
How much over-valued is the Saudi Riyal in the face of declining oil prices - which started in 2014?
4/
But the deepest trouble is that any break from the peg at this stage will create all kinds of massive balance sheet dislocations - a financial crisis of sorts.
6/
1) prevents SA from diversifying out of oil due to an over-valued ER.
2) forces SA to burn through reserves to finance a large deficit
3) inevitable break from peg will not be pretty