Suppose, for whatever reason, Napoleon dies in 1812, a year after his son was born. Say he falls off his horse on the way to Russia.
What happens now? Napoleon II would obviously be declared Emperor, with Marie-Louise as regent. Would the rest of Europe's powers accept this and agree to a lasting peace? Presumably, they'd prefer a Bourbon restoration, but that probably seemed unlikely at the time (when the Grande Armée was still essentially undefeated). This would be essentially a post-hoc acknowledgement of Napoleon I's right to rule, but having a Hapsburg regent could allow the young Napoleon II to be groomed to be "respectable" monarch.
If a peace settlement can be reached, what would it be like? Would France achieve its coveted "natural borders" (including the Rhineland and Belgium), or more still? France would be an interesting bargaining position, in possession of a lot territory but probably doubtful of its ability to hang on to much of it.