I'd rather comment further on immigration outside Quebec. Francophone immigration to Quebec definitely has the potential to expand and persist, to contribute permanently to French in Quebec and thus in Canada.
As I confirm in my brief, native Quebecers who migrate outside Quebec, in the same way international immigrants migrate to other provinces, become anglicized, starting in the first generation, at virtually the same rate as their host francophone society.
The example I cite is more than an example; it's a general rule. In British Columbia, the anglicization rate of Quebec immigrants—and half the francophone population in British Columbia are originally from Quebec—is 71% among those who have reached adulthood. The rate for international francophone immigrants is 65%. The majority in fact contributes to the demographics of the English-language population.