Well, the CSA was larger than many big countries and certainly had the resources/building blocks to make a go of it as a nation. Switzerland is smaller than Virginia and has endured for longer than the US.
But I think the chief benefit of a Southern victory would have been a tilt back toward the form of republican (small "r") government created by the founders; that is, a restoration of federalism and affirmation of state sovereignty. Probably the CSA and USA would have re-merged, but with the right of secession preserved as an essential check on the potential abuses of a centralized federal government that brooked no limits on its power (as created by Lincoln).
The slavery thing is a modern confection. The war was not about freeing blacks, much less giving them political and social equality (see "Honest Abe's" own statements in re blacks). The war was about state's rights and taxes (tariffs, specifically).
Lincoln was determined to force the states (and every American) to accept federal supremacy in all things - and to enshrine the corporatist state we suffer under today.