If Napoleon dies, than it's hardly "Napoleonic" peace.
Nevertheless- how long can Tzar flee from Napoleon forces, avoiding pitched battle? Especially with Poles setting their state on his westernmost lands? During November uprising Poles rose up to Kiev and Polotsk- if Napoleon gives them opportunity to build a new state, then they will do so. And Greater Poland will easily be able to field army equal to Prussian (which- I assume- will be dismantled by Napoleon). And Poles will be die-hard (and willing!) allies of Napoleon- if Russians win, then Poland will be partitioned again.
Also- why do You think that Napoleon have to win quickly? He can slowly attach pieces of Russia to Poland- shortening supply lines, weakening Russia and strengthening Poland. He won't give anyone opportunity to think that he's losing, because he won't be losing- Tzar will either slowly fall back or will be forced to fight in the field- but not like otl, with Grand Army lacking supplies and suffering from attrition.
Napoleon really didn't want to create an independent Poland. He used the hopes of others to get what he wanted, but never really created it when he had the chance. He always had the impression that the Tsar could be bent to his wishes and sacrificed strategy and common sense in this belief. If he creates Poland, well he's going to create even more animosity from Prussia, Austria and Russia. He needs a victory of some sort before too long, Austria will become restless, Prussia will be looking for an out and Spain will continue to bleed with his forces stretched throughout all of Europe. The supply situation was dire even before the Grand Armee set out as well.