Would the loss of Sankt Petersburg be more or less damaging to the Russians? (It was the capital after all). Because the place still looks easier to reach, even without seaborne supplies.
Look, I get that you, unlike most of us here, aren't an obsessive-compulsive military nerd (I'm included here, so nobody get mad), but people have explained. Let's say Napoleon goes to Petersburg. The Grande Armee crosses the border, defeating a few Russian detachments. So far, so good. But halfway up Latvia, things start to go horribly wrong. Rural resistance stiffens (this is not a time when the Baltic peoples wanted to independent AFAIK). Fewer and fewer supplies reach the army for some odd reason (i.e. Cossacks tearing the lines apart, the Prussians 'delaying' them). The British constantly bombard and harry his army. The men are hungry. It's cold, and the only homes that let his soldiers in without being forced are ones in which soldiers just don't wake up the next morning. Meanwhile, in the southwest, Kutuzov has the gall to march right into Napoleon's supply lines, cutting him off for good. Another Russian force, led by, say, Barclay-de-Tolly, threatens his army from the north; but every time Napoleon seeks battle from either, they retreat and let the other harry him like wolves harrying a bull. Winter falls--the coldest winter many in his army have ever known. Making a final, resigned decision, Napoleon retreats as fast as possible as his army simply dissolves around him. Unfortunately, as gets near Smolensk, Kutuzov falls upon his much-reduced force. Though Boney fights bravely, his men are exhausted and starving, and soon surrender. He's captured, and sent to Petersburg to be imprisoned.
Actually, that's kind of a cool idea; WI Napoleon captured by Kutuzov in 1812?
