You might be interested in my posts for this question. Briefly, Napoleon expected to crush the Russian army near the frontiers and thereafter disperse into winter quarters if the Tsar did not make peace.

The campaign failed because he wasn't able to destroy the Russian army. He planned the invasion well enough that the opportunity arose a few times, but each time it slipped through his fingers. This arose from his own indolence (the long pauses at Vilna, Vitebsk, and Moscow are quite uncharacteristic, as was his remarkable passivity at the field of Borodino), his poor choice of subordinates (his brother Jerome was probably not fit to lead a division, much less an army of his own), or his fixation on keeping the army concentrated, which inhibited the efficient gathering of supplies and in the end diminished his great numerical superiority.

Regarding siege warfare specifically, Russia didn't really have much in the way of fortresses; Riga was the only significant one, and it was well out of the way from his eventual line of march. Fortresses by this point in history had lost some of the power they once exerted over warfare in the 16th century. Armies had developed quite efficient means for the reduction of fortresses; Vauban practically perfected the art of siege warfare in the late 17th century, and 40 days was generally considered sufficient to reduce most fortresses. Moreover, the vast size of Napoleonic armies made it possible to detach forces to blockade fortresses without overly diminishing the active field forces.