I think most of the world learned their lesson after the first two. I think it will be more small scale wars like it is now. Localized stuff, started by some mad-man. Any future world war would be end of days stuff IMO.
Rogue nations are more of a threat because they're more likely to actually use nuclear weapons. However, I think the risk of another world war is slim, but not totally out of the picture. Like the saying goes, "I don't know how WWIII will be fought, but WWIV will be fought with sticks and stones." That right there is why the US and the Soviet Union never went "hot" ... MAD ... Mutually Assured Destruction. In other words, you bomb us, and we're going to make sure that there is nothing left of you, and vice versa.