It would have been a total mess and a disaster. But beyond that, I'd hate to guess.
Oh, this is the SECOND referendum, the one with a clear question. Ya, still... Hmm...
OK. there's a couple possibilities. 1) the referendum is a razor thin win for the Oui side. This gets really messy, as a lot of people in Quebec really want enhanced status for Quebec (what in other jurisdictions might be called an Autonomous Republic, what Quebec calls Sovereignity Association) rather than full independence. The Federal government would probably refuse to accept the result, and Federal/Provincial relations would drop to all time new lows. Quebec would proclaim a UDI which France would recognize - but likely few other countries. Feds pull offices out of Hull, causing a massive local depression...
2) the margin is, say 55% Oui (probably ASB, but possible).
I cannot see the government resorting to force for several reasons. 1) the Canadian Armed Forces aren't large enough to hold down an entire rebellious province (well, PEI, maybe)
2) the Forces have a disproportionate number of Quebecois - many of whom would refuse to fight their natal province.
3) It's just not the Canadian way - any PM whose first thought was violence would likely be thrown out of office by his own party - let alone by the electorate in the next election.
What I can see is a whole lot of dithering and negociation. I think the Federal position in negociations would be 'OK, we accepted the will of the people, you can go - as long as YOU accept the will of the people. You lose all of Northern Quebec (Cree), Eastern Townships (Anglo), (parts of) Montreal (anglo & allophone), the Outaouais (anglo, close ties to Ontario)' And/or 'you came into Confederation with a thinnish strip along the St. Lawrence, you can leave with the same land'.
Oh, and Quebec would be startled to discover that some of the protectionist measures she can get away with INSIDE of Canada would be illegal under, e.g. GATT! Nor would she automatically be dealt into NAFTA, which she just assumed she would.
I would imagine that there would be a rather dramatic repealling of bilingualism, almost immediately. Quebec citizens would lose their Canadian citizenship (yes, they thought they could have both!).
What happens to RoC (Rest of Canada, not Republic of Canada) is a very good question. Certainly the lack of connexion between the Atlantic provinces and Ontario and the West would lead to problems. So, too, would the rather overwhelming dominance of Ontario.
I can certainly see several 'Canada's forming over the course of the next 50 years - nothing immediate.