I'm afraid I'll have to really disagree on this one. The end result (40-50 years) would be an even smaller Quebec/Canada, largely limited to the french dominated area that became Lower Canada and maybe the eastern reaches of Upper Canada along the Ottawa Valley.
There's nothing saying that Pitt wouldn't have simply equipped another army the next year. Wolfe's army was only one of three or four armies operating in North America that year.
Leaving that aside...The problem is that Quebec was a prestige side-show to the French, which probably cost more than it generated...witness Voltaire`s comments about a few acres of Snow. ON the other dside of the coin, the demographics of population and emmigration were heavily in favour of the British in Eastern North America, even if you posit consistently bad generalship for the English. By 1759, there are about 20 English subjects for every French subject in North America.The French could build forts anywhere they liked but they then had to defend them, without a local base of support beyond the Native population.
The Americans were already poised to pour into the Ohio River valley: that is what started the French and Indian War/Seven Year's War in the first place. An French-controlled Quebec may not mean any proclamation line in the north. I doubt you`d see active British support for settlement accross the Appalachains, but equally, I don`t think you`d see them trying too hard to stop it either.
Even if the 1759 campaign had failed, you have to remember that the fighting was being done in Quebec, not the Ohio valley...so to that extent, the French had already lost effective control of the link between Louisiana and Canada. British troops had already cut the French links to the Great Lakes, when they captured Kingston/Fort Frontenac the previous year, so long-term French control of penninsular Ontario is somewhat suspect.
Assuming the rest of the Seven Years War went along as scheduled, a French-controlled Quebec would only remove one of the causes of the American revolution but it would significantly change the face of that war, with no British base in the north. My guess is a much more focussed Southern Strategy right from the beginning, with a neutral Quebec sitting out the initial phases. Very different war indeed.
After that the butterflies are just too many...Does France enter the American Revolution...Does the French revolution happen...what role would a French Quebec play...would the *Americans (independent or as British subjects) buy or conquer Louisiana...
David