Duminy yes, McKenzie no. Quality batsman, might fail but might just as well come good.Can't see it happening. They basically have two weak links in their lineup (McKenzie and Duminy) which puts huge pressure on one batsman to make a big ton.
It will be a big chase, but with Smith / Kallis and to a lesser extent Amla / De Villiers / McKenzie they do have the firepower to pull it off. Personally think they will fail, though, and will blame it on the absence of Ashwell Prince.