I guess they assume that without being forced, no one would actually speak French.
In the long run, that's not an unreasonable assumption. Languages are, after all, tools for communication. If you could go to school and take your lessons in English, if the coolest TV shows and movies came out in English first, if speaking English gave you a better choice of good jobs... then, over time, first people who spoke French at home but learned English very early in life, so they spoke it well, might end up living much of their lives in English, maybe even marrying someone who doesn't speak French, so they speak English at home, and their kids only speak English.
After all, the Quebecois can look around them, and ask how many people speak Inuktitut and don't understand English.
To preserve French in Quebec eternally, Quebec does need to be a country, so that the Quebecois would need landed immigrant status to take English-speaking jobs in Toronto. But they would have to give up the Eastern Townships, they would have to sign treaties with the United States and Canada on the rights of First Nations people (Native Americans), and Montreal would have to be partitioned.
There is no way many ordinary English Canadians would accept that some of its people would become subject to a foreign French government. But some Quebecois have vowed a campaign of terrorist violence if any part of the sacred soil of Quebec were divided from it.
So, instead of becoming an independent country, they stand a good chance, if they vote "Oui" on a referendum, of becoming as independent as the Palestinians are of Israel. (It's by no means a certainty; we don't have many politicians of the type that will fight rather than endure any compromise of freedom. To help ensure English Canadians in Quebec will meekly submit should Quebec separate, we have strict gun-control laws.) But, then, nationalism was never rational.
