Pell knows his history. When Protestant zealots burned down the Catholic cathedral in Philadelphia, the cardinal in New York responded by putting a guard of a few hundred hardass Irishmen with sledgehammers, shotguns and boards outside St. Patrick's.
I think Archbishop Pell would request assistance from local volunteers in an organized way if the police response was inadequate.
Now that would be downright refreshing...because, from all I have read over the last week (particularly Tim Priest's assessment of the police "service" in NSW), the authorities don't actually have any history of standing up to the ME gangs.