Tough call, you should run some numbers. Selling will make you liable for capital gains tax. You're not a resident, so it will need to be a very big profit before it takes effect though. But then you need to look into the investment returns. If you move the money out of SA for investing, it'll cost you about 1% in fees. Then you'll also have to pay dividends tax on the returns. I believe the global average for stock market investments is 6% over inflation, does that make it worthwhile for you compared to the airBNB returns after tax? airBNB will be a little more work, but if you have a reliable person in SA to manage it then it won't be too much. Your location is probably prime for it.
AirBNB are fantastic to deal with. My wife airBNBs our place. 3 days of bookings pays for the levy, rates, taxes, water and electricity. If we get 10 days bookings it pays for all the above and the bond too.
We've had a couple of issues to deal with, I'd say 1 in 5 guests do something we don't like, and 1 in 10 are horrible. In all cases though airBNB has gone totally above our expectations in resolving issues for us.
We also stay in airBNB places when we travel, and once arrived to a dump, complained the next day and they refunded us in full and helped us book another place. Even though the next place was more expensive, they paid in the difference. Such a pleasure working with them!