I actually think it will be the reverse. I think there will be a riot if he (Obama) wins, much like what happens after a city wins a major sporting event.
Also, I think a riot would have ensued if instead of Gore, Obama had lost Florida back in 2000. That would have made many feel that the "white man" fixed the election. I guess since Gore and Kerry both lost in consecutive elections, by the slimmest of margins, that if Obama were to lose in the same fashion today that it wouldn't have such a big impact.