This just shouldn't have been an issue. Pilots cannot go past 20 hours. Departure was obviously looking tight, but still worth a look. And that's with Sydney as the destination. You can always go to Brisbane and save 45 minutes or so, or perhaps go to Fiji and save a couple of hours, but still have the jet within reasonably easy recovery range.
I suspect the Captain would have been stunned by the lack of thought from the back end, and can only hope that if the story as told here is true that a couple of CC are looking for other employment.