If they could make 264 for the loss of 4 wickets, then they will make another 200-250 with the loss of the remaining six wickets. In the first innings they had a lead of 46 runs, so the target for South Africa will be in the range of 500-550, which is going to be impossible to achieve. But this series have been full of twists and turns and if South Africa can get the remaining England wickets for another 30-35 runs, then the target will be within the achievable range and they will have a go at it.
BTW, Australia looks comfortably placed in their match against New Zealand. The Kiwi bowlers are not offering any sort of resistance and Warner have made his 24th test century. Labuschagne is currently on 57, and I won't be surprised if he also hits another century. Matt Henry and William Somerville are looking completely clueless and surprisingly Neil Wagner isn't being used much (another injury?). This is going to be one of the most one-sided test match between the two sides.
Unbelievable start for the second innings of NZ. In first innings they lost first wicket at 68 and now they are already 5 wickets down for score of just 44 runs. NZ still require 372 runs to win the match which does not look to happen and OZ winning this match easily again.