The consensus among the scholars I've read is that the South may well have won - even a sustained stalemate would have constituted a victory - had it managed to break the blockade and establish commercial relationships with the European industrial powers of the time, specifically Britain. Simlar to how French aid helped us in the revolution.
In reality, I think the South could never have won a clear victory. The Civil War was the first modern war, and it's clear that the South did not have the wherewithal -- people, resources, and industry -- to properly fight it, whereas the Union did.
Let's be quite clear: the North flat out won the war, and the South flat out lost it.
The only "victory" the South could have won is an armistice born of war-weariness on the part of the North. I think however, that the war would eventually have started again, for the same reasons, though probably more in the west. And the South would have been defeated by the North, for the same reasons.
Had the South attempted to sustain guerilla warfare, it is likely that Southern resistance would have eventually led to some sort of deal being struck. Southern guerilla operations were usually rather succesful- small, capable groups of light horse for example- in destroying Union supplies and demoralizinf occupying forces. With the addition of men- based around their homes- engaging in non-conventional attacks on railroads, supply depots, camps, and the like, then fading into the woods or general populace, even greater damage could be done, and this style of operation continued even after the last area of Confederate military control collapsed. Eventually, with casualties and war expenditures mounting, the Northern populace would become weary of a war in which there seemed to be no signs of victory, and one in which, were there victory, they were unlikely to profit much- which was the case in the West, where the subjication and destruction of the indeginous tribes meant an opening of free land and immense stores of wealth. There, long, seemingly victory-less campaigns were more politically feasible, and in the end more likely to succeed, as Indian populations were small and often poorly equiped.
However, the Southern leadership recognized that a war of guerilla tactics was likely to leave the South in ruin far greater than the late war, and thus, wisely I think, chose to completely disband their armies and sue for complete peace and a total end to hostilities.