They were only missing Starc and Cummins while Hazlewood, Zampa etc played which is why they were only missing a couple of their regular bowlers. All of their key batsmen were playing though.
I doubt it would have made a difference even if Starc and Cummins played since their batsmen collapsed like dominoes primarily thanks to Maharaj.
Now if Australia lost the first match because of Pat Cummins and Mitchell Starc, then Australia will lose the second match too, especially since these two players are out of the squad. Moreover, the Australian batsmen were defeated in the first match by the extraordinary bowling skills of Kesev Maharaj.
There will most likely be no change in South Africa's second match, so it will be very difficult for Australia to level the score by winning the second match. On the other hand, if South Africa performs like we saw in the first match, then South Africa will definitely win the second match.