That is why, as a general rule, every year they "discover" approximately the same amount of oil they produced/delivered that year.
But maybe they'll "settle" for less. After all there is money to be made, the haggling is just about the price.
Counterintuitively, a high price may actually be scarier for SA than a low price. It may cause competitors to invest in exploration. And where fixed, initial cost make up a large part of costs, some competitors may continue to produce even if prices fall, and even if the investment was based on wrong estimates and may never actually reach break-even.
SA running out of oil would also hasten efforts to replace oil with renewables.
The typical reason for an IPO is a company in its early life phase which needs money to grow. There is no lack of cash in SA, so why would they sell off Aramco, if it had a great future?