This is exactly why I have a Delta flight booked as backup. We have an upcoming flight from IAD - ACC - JNB on Dec 10 and thankfully I have status with Delta and I can hold another reservation without consequences. I am going to send United (since I booked the SAA flight with United points) a twitter message and see what they say. My options out of IAD would be Ethiopian or Lufthansa....
Also thankfully my flights from JNB to Muan Bots are on Air Bots.