TBH, Napoleon was already in a precarious position before Waterloo. While Waterloo was a sad end to the most glorious regime of all time, it was just the hard end of a fall which began with the retreat from Russia.
I am not sure about Gettysburgh, whether it was similar or different.
IMO both conflicts (the Napoleonic Wars and the Civil War) would have given birth to a very different world should their conclusion have differed from what we know. Napoleon's victory would have made the French Empire the 1st world power for the whole of the 19th century, with the USA as its biggest ally. The whole world would be speaking, trading and thinking in French; like English is used today. Religion would be a thing of the past, and colonialism would not have happened in the form it took under the Brits, or maybe not happened at all. Forget about WWI and II too, cause a French dominion over continental Europe would mean no real power would be allowed to emerge and challenge it. There would have been no Holocaust either.
I'll leave it to y'all Americans to help us imagine what a Confederate victory would have brought about, be it positive or negative.