Buster
Conmankiller is right, they will pursue you. The debt will be passed to a company who will carry out international searches and once located, they will employ collection agents/lawyers in South Africa.
I have read of people being pursued in many parts of the world, EU countries, India and the US. Another poster mentioned that they were having difficulty getting a credit card in Asia, as the banks there carried out searches on their UK credit history.
My advice for what it is worth, is to get your financial arrangements in South Africa sorted out first. e.g. Bank Account and Credit Card. Then come to an arrangement with the companies you owe money to, to make payments. If they know you are leaving the country they may be willing to accept a lump sum full and final payment, for a percentage of the amount owed. This is a lot better than messing your credit record up and then being hasled in SA.
Huckster