If (assume the plausibility of this scenario) Lee had taken Porter's advice, and dispersed his AoNV into guerrilla bands to avoid surrender, and the other Confederate armies followed suit and successfully turned partisan, could the Union still eventually have won a permanent victory? By "winning", I mean a permanent cessation of rebellious activity in the former Confederacy that is popularly accepted as legitimate by the inhabitants. To accomplish this, the Union is allowed to use any means, including reprisals against the civilian population and other extreme measures, up to and including the abrogation of its own democracy, as long as the nation is preserved.