Do you think Stalin would have quit even if he had lost Moscow? That loss didn't finish the Russians when Napoleon invaded.
You're right, it didn't. In fact, that loss finished Napoleon.
Moscow had mostly been abandoned by the Russians and Napoleon's army was killed by the cold.
Indeed, Stalin did have plans to move deep into Siberia if he lost Moscow. If so, he might have stayed there for a while, licking his wounds. Also, he would have been effectively cut off from resupply by the West, which is what kept the Soviet Union in the war for a while. If the Germans had managed to isolate him there, then they would have had a much better position.
Of course, its all academic speculation.