It happened in Louisiana in about 60 years and Louisiana had state rights. It was a loose federation, far looser in the United States at that time than Canada today. Louisiana's
culture disappeared under the pressure of economic and business forces within about 60 years.
I suggest that were Quebec to separate and not have the genuine partnership that exists in the Canadian Confederation today, especially with the Americans just south of the border, there would not be anyone speaking French anywhere in the business community of Quebec. That would be a shame because it would be the end of a culture.