JOHANNESBURG—Amid the back and forth early Wednesday between SABMiller PLC and Anheuser-Busch InBev NV over a possible tie-up, one question making the rounds here has been settled: Any combined company will keep a stock-market listing in SABMiller’s ancestral home of South Africa.

Before Wednesday, investors worried that their homegrown corporate giant might be leaving their wobbling economy for good, depriving them of access to a…