Militarily? Who would invade La République Québecoise?
Canada
Perhaps he means diplomatically: Quebec's language laws would return to how they were before the Canadian Supreme Court said that banning all languages except for French in public places wasn't legal. The result would make Quebec a pariah state
Quebec's economy is a mess basically. It is propped up by Government subsidies (of which it gets a lot more than it's fair share, something that pisses of people in the Maritimes) most federal contracts are done by Quebec etc. etc. etc.
No subsidies=economic disaster
Another problem is that the the Shipping industry (including PMPM's company) in Montreal would get the hell out as soon as possible: it's run by Anglo's and Federalist Franco's (about 25% of Quebecers would leave Quebec if it became independent...) Montreal could become redundent as a port very quickly.
And then there's Aluminum. Because of Hydro-Quebec (and that's another problem: who's going to buy electric from a Pariah state?) Quebec has a huge Aluminum smelting industry (along with by-products like wire, trains... etc) much of which is based in the PQ stronghold, the Saugeney Valley.
Quebec doesn't have any Bauxite (it's imported from Jamaica and Guyana, both are Commonwealth Countries, BTW) and much of the industry might be re-located to Labrador or Northern Ontario... devastating the economy of the most staunchly seperatist part of Quebec.
There is no case for independence based on economics (most Quebecers know this) it's based on the emotional pull of dodgy history and a "superiority complex"
Dunno about that: a lot of Canada would do well out of Quebec leaving (the Maritimes, Northern Ontario and the Praries) as they'd get more federal subsidies, support and stuff.