Fully a quarter of Canada's population would go. Nearly $170bn of goods and services generated yearly would no longer come into Canada's accounts. The rump of Canada would be divided in two, with the tiny maritime provinces physically cut off from their co-citizens in Ontario and the west.
The prospect has unsettled financial markets, pushed the Canadian dollar lower and convinced many Quebecers to shift their savings to banks outside the province. The most alarmed among the population predict an economic meltdown, not just for the departing Quebec but for the rest of Canada.
Worse, they feel, any subsequent negotiation between an independent Quebec and the rump of Canada would create insurmountable tensions. For a start, it is not even clear who would represent Canada in any talks. The Prime Minister is Jean Chretien, a Quebecer. He represents a Quebec riding. Seventy-five seats in the House of Commons are held by Quebec politicians. In a country where the relationship between the provinces and the centre is usually tense, who would speak for the rest of Canada in any negotiation with Quebec on the terms of divorce?
Yet despite all these worries, fully half of Quebecers (and a majority of the Francophone voters) are telling pollsters they will vote "Yes". If they prevail, Quebec will take up to a year to negotiate the terms of the split. If the negotiations prove fruitless, unilateral independence will be declared. Legal or not, few expect any attempt - in the courts or through more violent means - to halt the process.
The two key figures on the separatist side are a study in contrasts. Jacques Parizeau, the Quebec premier, is a patrician gentleman with an English accent procured during a stint at the London School of Economics. Blunt and sometimes bizarre in his public utterances, he is not as popular in Quebec as his cause. Lucien Bouchard, the former Tory turned sovereigntist, leads the mighty Bloc Quebecois, the official opposition in Ottawa, dedicated to Quebec independence. A bout with the flesh-eating bacteria cost him a leg but gained him nearly mythical status in Quebec. He appeals to the "ordinary Quebecer" with his mix of plain speaking, passion and pithy turns of phrase. The cause they espouse has the support of half the province's population, a figure that shocks the rest of Canada.
Why do so many Quebecers want to go? What can be wrong with a country that tops international competitiveness surveys, that boasts one of the world's best-educated workforces and a universal, affordable health care system? Why would a people so blessed by natural resource wealth, a modern transportation system, a massive market on its very doorstep in the form of the United States and a non-violent political and civic life, want to throw it all away on a roll of the dice, on an unknown and divided future? Surely separation is a disease of the Balkans, an extreme political decision more closely identified with a Czechoslovakia than a Canada?
In fact, there is a real malaise in the True North, one that has affected many other countries where different cultures, language groups and "ethnicities" have been forced, or have chosen under duress, to live together. To understand why Quebec nationalism will not go away and why there is a chance, if not this time then perhaps the next, that Quebecers will choose to go, you have to look at the history.
The country's birth in 1867 was the coming together of two founding peoples, the descendants of the settlers of New France and the victorious British, who vanquished the French army on the Plains of Abraham in Quebec city in 1759.
Rather than force the losing side to assimilate, to bury its culture and traditions within the bosom of the larger and stronger side, the British instead allowed the French minority to establish separate Catholic, Francophone schools and retain a different legal system (Napoleonic, not Common Law).
Over the years, but particularly since the Sixties, the Quebec government has exercised more and more powers: to collect its own income taxes (the only province to do so); to run its own pension fund; and to develop a stand-alone welfare system, albeit one financed by transfers from Ottawa.
Despite this "sovereignty by stealth", Quebec has seen the separatist option remain popular with a solid 40 per cent of the province. Nor has this separatist voice been quiescent. It has enjoyed a highly active presence for a long time now: from the 1970 terrorist bombing campaign of radicals to the election of an avowedly separatist government in 1976, to the high drama of myriad constitutional wranglings in the Eighties and early Nineties.
What does Quebec want? The question has dogged federalist politicians for the 128 years of Canadian federation. It is indisputably the fact that Quebec is another country: different language, different elite. To be Francophone in Quebec is to yearn to be "maitre chez nous" (masters in our own house). Said one Quebecer last week: "We have been paying rent for so many years. We want now to buy the house."
Reason might dictate maintenance of the status quo: a common currency, a common market and common destiny with the rest of Canada. But emotion wants other things: protection of the French language, a chance to live a la francaise in North America. Many are prepared to risk wrenching economic dislocation in the short term for the prize of sovereignty later on.
A "Yes" vote would usher in a period of chaos and danger: enormously unsettling not only for Quebecers but for other Canadians, too. Not least of the pressing questions sovereigntists must ask themselves are the following thorny issues: who gets a Canadian passport; can an independent Quebec use the Canadian dollar, as the ruling Parti Quebecois insists; are the borders of Quebec to be retained; can Quebec effortlessly join Nato, the North American Free Trade Agreement, even the United Nations; and what about the minority Anglophone, immigrant and aboriginal communities within Quebec who are uncomfortable with the nationalist sovereignty project?
The break-up of Canada would also have a destabilising effect on other countries that harbour significant minorities. It is one thing to see Eastern Europe erupt and subdivide, but quite another when a country such as Canada succumbs. The signal sent to the minority Basques in France and Spain, for instance, or to the Welsh and Scots in Britain, would be unmistakable: modern, advanced democracies can and do break up. If a rich, modern, peaceful country such as Canada can fly apart, ignoring the efforts of 100 years of partnership and compromise, then what hope for the rest of us?
If the vote is "No", then some hard work will begin. Canada will have to decide how to include Quebec; how to keep Quebecers from feeling marginalised. By all accounts, nearly half of them do not like the status quo and desire some form of sovereignty.
In order to survive as a united country, Canada will have to prove to Quebecers, once and for all, that they are an important part of the whole and not just an accident of history.
History of an uneasy union
1867: British North America Act. Upper (Anglo) and Lower (Franco) Canada are united in a confederation that by 1949 included 10 provinces and two territories, with a balance of powers struck between the federal and provincial governments.
1912: Statutes of Westminster. Like other British Commonwealth holdings, Canada gets a greater degree of autonomy, shared between the federal and provincial governments.
1941: the Conscription Crisis. Quebec does not want its sons to fight Britain's war, but Canada insists.
1970s: emergence of new funding arrangements, including the creation of an equalisation system to smooth out regional variations in welfare, education and health.
1971: Victoria Conference, when Quebec premier Robert Bourassa outlines Quebec's historic demands for being treated differently from the rest of Canada. Prime Minister Pierre Trudeau introduces the Official Languages Act, an attempt to make Quebecers and anglophone Canadians feel welcome across the country. All federal agencies would henceforth offer service in either official language, and millions of Canadians students would be paid to learn the other official language.
1976: Rene Levesque, Quebec's first separatist premier, is elected. The infamous Bill 101 is introduced, mandating French as the official language of Quebec and restricting access to English schools and the use of English on commercial signs.
1980: Quebec says no in a referendum to a request by the government to be given a mandate to negotiate a new constitutional arrangement with the rest of Canada. The federalists promise to attend to Quebec's needs by patriating the constitution to Canada from Britain.
1982: the constitution is patriated to Canada and a new amending formula agreed, with the support of nine out of 10 provinces. Quebec doesn't sign, and feels betrayed when the Supreme Court allows the project to go ahead.
1987: Prime Minister Brian Mulroney negotiates the Meech Lake Accord, which gives Quebec a constitutional recognition as a "distinct society" within Canada and confers additional powers on Quebec and, by extension, other provinces. Fillibustering in Manitoba and the opposition of Newfoundland premier Clyde Wells kills the deal.
1992: Charlestown Accord, a "super Meech Lake," is put to all Canadians in a referendum. They reject it, not only in Quebec but in many provinces.
1995: Quebec government launches the latest "sovereignty" referendum, with the most recent polls suggesting that 50 per cent will vote "yes".