Edit: nevermind, it seems that he decided to attack again on the third day instead of retreating.
Yup. Plus Napoleon's advisers even before Leipzig advised him to flee to France to defend the Empire through Italian Alps and the Rhine. But Napoleon didn't want to lose his power over Germany something he spent years trying to get. He also believed that he had a chance of winning which was true. He almost won the battle, and had he done so, France would have likely had its Empire preserved.
Austria would likely be scared white with an angry Napoleon bearing down upon them. Prussia depending on the state of Napoleon's army might also find itself overrun as there were other garrisons of troops all stationed throughout the fringes of the Empire like the Duchy of Warsaw.
I’m wondering who Napoleon II is going to marry, since I’m OTL, he had a close relationship with Princess Sophie of Bavaria
There was some speculation that Franz-Joseph's brother, the Archduke and later Mexican Emperor Maximilian was the son of Napoleon II as the result of an ongoing affair between Napoleon II and Princess Sophie. The Habsburgs' enemies certainly played up that rumor. Though this rumor is likely false as Napoleon II was six years younger than the Archduchess and closely monitored by Metternich. I doubt Napoleon would have done something so stupid like that to disgrace himself and destroy his already precarious position. I'm not quite sure who Napoleon will marry just yet, but I think it will be more or less after he takes the throne since he's only in his early 20's by the time of the 1830's. I'm open to ideas if anyone has them.
Any chance young Bismark teams up with Napoleon 2 down the line?
Unless bismark ends up working for Austria then no, i don't think so. Prussian ambitions for a prussian lead 'small Germany' were directly opposed to Austrian and French interests, which combined with François' bonaparte and hapsburg background mean that he's their ideal arch-nemesis, at least as far as propaganda is concerned.
Unfortunately this likely wouldn't occur as Bismarck was a devout Prussian and monarchist. In otl a young Bismarck raised a Medieval style peasant army from his lands in defense of the Prussian King when he was held hostage by a group of armed Revolutionaries in the Capital. Of course during his march on Berlin he was turned down by the actual Prussian Army who didn't want an untrained peasant mob making things worse.
Not to mention Bismarck is very, very conservative, in comparison to the more liberal Bonapartists.
Napoleon I himself was quite conservative as well. He hated La Marseillaise for instance and had initially banned it, but played it when his armies were marching through Germany to present himself as the embodiment of French nationalism abroad. Napoleon I's strand of Bonapartism is essentially a Roman style concept of popular autocracy in the manner of Caesar. Though Napoleon II however was a man born into the world of his father while also being raised in the Old World values of his grandfather the Habsburgs. Augustus was quite conservative in comparison to Caesar, and presented himself as restoring Rome back to its tradition and past when times were good. Though I can see someone like Louis-Napoleon becoming the leader of the more liberal Bonapartist faction.