They'd have to re-introduce dingos in significant numbers, which has other possibly-negative effects. If they stopped farming animals altogether and simultaneously re-introduced dingos in significant numbers, then maybe they could pull it off, but I highly doubt animal farming is on the verge of ceasing entirely in Australia.

The problem is that dingos were removed from the majority of the continent because they were a threat to livestock. However, dingoes were the only predator of the kangaroo. Kangaroo populations are now out of control, and only aggressive hunting keeps the kangaroos from totally destroying the environment. If they didn't hunt them, roving kangaroo herds would overgraze and turn huge chunks of Australia into barren stretches incapable of supporting any other wildlife.