Steven Pinker describes how that went:
> "As a young teenager in proudly peaceable Canada during the romantic 1960s, I was a true believer in Bakunin's anarchism. I laughed off my parents' argument that if the government ever laid down its arms all hell would break loose. Our competing predictions were put to the test at 8:00 a.m. on October 7, 1969, when the Montreal police went on strike. By 11:20 am, the first bank was robbed. By noon, most of the downtown stores were closed because of looting. Within a few more hours, taxi drivers burned down the garage of a limousine service that competed with them for airport customers, a rooftop sniper killed a provincial police officer, rioters broke into several hotels and restaurants, and a doctor slew a burglar in his suburban home. By the end of the day, six banks had been robbed, a hundred shops had been looted, twelve fires had been set, forty carloads of storefront glass had been broken, and three million dollars in property damage had been inflicted, before city authorities had to call in the army and, of course, the Mounties to restore order. This decisive empirical test left my politics in tatters (and offered a foretaste of life as a scientist)."[16]
The idea that this incident demonstrates that any city will go up in flames immediately if the police take the day off is a misreading this specific moment in history.
See: https://en.wikipedia.org/wiki/Murray-Hill_riot
That's not to dispute the idea that cities will generally retain order if police are absent. I imagine it varies wildly from one time and place to another.