My thinking goes here like this: Russia and France are so far from each other, that logistically/politically it isn't feasable to war with each other. So had the Czar sued for peace, what kind of guarantee would Napoleon have got so he doesn't have to come over every year and make sure the Czar keeps his word (of not trading with England)?
Since the 2 countries weren't next to each other, taking away territory wouldn't have worked. I think the Czar could have just lied to Napoleon and not kept his word 6-10 months later.
In this era, to sue for peace after the start of hostilities generally required that the supplicant to agree to pay large financial tributes to the victor, to hand over the control of territory, and/or to accept garrisoning the troops of the victor in their lands. The Treaty of Tilsit (France's prior peace treaty with Russia following Friedland) was quite generous to Russia, a reflection of the fact that Napoleon was attempting to get on Tsar Alexander's good side and make him an ally against Britain and to join the Continental System. Napoleon invaded Russia in 1812 after Tsar Alexander had reneged on his promises to adhere to the Continental system, and thus it would be unlikely that Napoleon would agree to an end to hostilities without substantial concessions from the Tsar. And while France and Russia may not have bordered each other, French-allied countries or territories did border Russia (Grand Duchy of Warsaw and Austria). These had contributed substantial numbers of soldiers to the Grand Arme in 1812, and the Tsar would have been expected to have made concessions to them if he had sued for peace.