It is close to ASB to have Napoleon win the campaign/war - enemies were not just too many, but also too good by 1815.
It is much debated how good Napoleon's army of 1815 was compared to earlier ones. I think we can say for certain that it wasn't the best and it wasn't the worst, but no matter where in between, the allies by 1815 (actually years before) had catched up on the French in doctrine, leadership, flexibility etc.
So the happy (French) times of 10 years earlier, where numerically inferior French armies could outmaneouvre allied armies and decisively defeat them was over for good. With Napoleon in charge the French could still inflict defeats on the allies, but a truely decisive military victory (no intact enemy main army afterwards) hadn't been achieved since 1806. Not because the average allied soldier had become better, he on the contary had moved from a professional to a sometimes reluctant conscript, but because the allied had learned how to organise and lead a big army in the field. This made it practically impossible for Napoleon to achieve anything more than limited tactical victories - which means war until one part has had enough and quits - i.e. attritional war.
20 years before, when France's economy and demographics had been devestated by 20 years of war, France might have had a chance in an attritional war (it did so in OTL), but by 1815 with the battles being fought on French ground - it is over!
It is of course not impossible to have Napoleon win Waterloo, it was a close fought thing, but apart from ASB intervention, he is not going to anihilate the British and Prussian armies and repeat the trick against approaching Austrian, Russian and German armies.
If Wellington and Blücher are forced from the battlefield, Napoleon will have to turn his attention/main force against the other allied armies ASAP. Even if he gain another tactical victory, there will still be a handful of other armies just as big closing - something like the 1814 campaign - both sides have bigger and better armies - but there is no doubt about the eventual outcome.
Left is the political scene - will one side panic? In 1813 the allies had shown that the alliance could not only survive defeats, but even grow stronger - from 1813 the allies simply had a very robust determination to get rid of Napoleon. The French also gathered behind Napoleon with surprising zeal - but after all it was them brealking first in 1814. Davout's post in Paris might mean all quiet in Paris as long as Napoleon is in the field with an intact army, but keeping Paris quiet won't win the war - only avoid defeat through collapse. Napoleon finding it necessary to leave his best and most relaible commander in Paris point to the French political determination being the most fragile.
But a British-Prussian defeat at Waterloo will probably nevertheless change the world into something inrecogniseable. The two main conservative powers, Austria and Russia will rule over the European continent - only challenged by each other - and with UK focussing on its Empire. Prussia will just be a Russian client state, and most of the rest of Germany and Italy will be Austrian ditto - the German unification as we know is very unlikely - and with it WWI and II as we know (but don't miss) them.
We will probably still see burgeois emancipation movements and unrest as well as nationalistic forces by the mid 19th century, but the conservative monarchies, many of them multinational, have a much better chance of withstanding the pressure - especially as there won't be a militarily strong Prussia to beat out the pride of their armies and crowns.
Emmigration to America will, if possible, be even stronger in this ATL, and if the conservative powers survive first the burgeois and next the communist challenge, USA and Europe (the Empire(s)) are probably going to be active antagonists - I actually wonder if Darth Vader is modelled on Metternich?
Regards
Steffen Redbeard
