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In addition the Napoleonic Empire (as opposed to Napoleonic rule in France proper) is doomed to implode. The Revolution and Bonaparte encouraged nationalism and it would bite them in the face.
This. If you aren't French, the rhetoric of "liberty, equality, fraternity" doesn't go well with "taking orders from Paris."
I suspect that if Napoleon's empire stood for any length of time, it would be replaced by new republican governments, not by a return of the old dynasties. Mid-to-late 19th-century Europe would end up looking like a lot like modern Europe — republics, and the occasional very limited monarchy, with boundaries that roughly follow the dominant language. (At least where that's possible. Where it isn't possible, such as the Balkans… things would probably get messy.)