It's sufficient if Australia believes that Facebook's existence itself is in violation of Australian law. In this case, an fine that is too much to be paid would force Facebook to exit Australia entirely.
Additionally, Australia would probably come down hard on any attempts for Facebook to market or solicit customers within their nation.
If a government of a country defines a website illegal, then that website simply will not be accessible from that country, end of story.
The US, despite leading the charge vis-a-vis the MPAA, has speech laws that make website blocking and censorship extremely difficult.
Facebook Ireland operates Facebook in Australia.
https://www.smh.com.au/business/companies/how-facebook-austr...
Well that would be a dreadful outcome for Australia, and I don't see anything indicating that is a potential outcome.