You can almost see the demographic cost of secession in this chart showing the shift of the population in Canada from 1980 to 2014. The sovereignty referendums of 1981 and 1995 did great things for establishing a sense of home rule for the French population of Quebec which had long chafed under English dominance from Ottawa and its own powerful anglophone minority. In exchange for not slashing the country in twain, Quebec got protection for its language and the ability to administer its own educational and health systems.
But a whole lotta companies left Montreal for a place that was more interested in trade than passing laws about the font size of English versus French. Ontario, long the manufacturing powerhouse of Canada, took primacy in business matters and became the headquarters of many companies formerly located in Montreal. Hence the flows of population toward Ontario throughout the period.
The other winners are clear. The thriving energy sector and solid environment for business made Alberta a net receiver of population, while British Columbia grew due to it apparently being extremely nice.
That’s not my most serious economic development analysis, but it’s probably accurate.