You're doing a whole lot of guessing, and ignorantly too. The South had already began to establish it's own international trade contracts with Great Britain sans tariffs. In fact, not much would have changed because the one of the North's largest industries was building ships and operating the slave trade. Yeah, Leftists, the North did that. Even as separate countries, they would have resumed business relations as many warring countries do after hostilities have ceased.
I studied economic history in university for an honours designation for my major in economics, though I have to admit, I had to drag out my old textbooks to refresh myself on the tariff structure at the time. Tariffs had been falling since the 1820s before the Morrill Tariff was enacted.
I am speculating on a counter-factual, it's true, so who knows what would have happened. However, the South was an agrarian economy and had little manufacturing. Great Britain wanted free trade with the South to feed the mills of the Midlands, and the financiers of London and traders of Liverpool benefited greatly from the flow of trade that sent arms to Africa, slaves to the South, and cotton from America. There is little to suggest that manufacturing would have sprung up in the South, since there were few cities of population density necessary to make the economics work, at least for the first 100 years after the Civil War. But since the South would have been reliant upon world markets, and given the reaction to South Africa, its likely that the South would have eventually been shut out of markets for their products as occurred with South Africa. The manufacturing and population migration from the unionized northeast most likely would have been diverted from the South to the Southwest since the laws in the Southwest were similar to the South.