Since the French and Indian War was really just a single theater of a much larger conflict between France and Great Britain, I don’t think a loss in that theater of the war would have been a major setback for the British or the colonies’ westward expansion. The French were very late to decide to colonize North America, though they exploited the fur trade fairly extensively with a minimal voyageur population of mostly single men. The British colonists, on the other hand, were a growing force.
In fact, British performance in the war in North America was one of the keys that brought the Pitt government into power in Great Britain, so that really set the stage for the American Revolution in any case.
Losses in North America would have, at most, delayed the westward migration of the British colonists. Without a strong and permanent presence at the frontiers to enforce the borders, the French would have eventually lost the territory to the migrating colonists – sort of like the Americans are now in our own Southwest.
I think another way to look at this is: What would have happened if the British had thoroughly digested and incorporated the lessons that should have been learned from their poor campaigns in the American woods, and brought those lessons to bear during the Revolution later?