As the title says. What if Napoléon had managed to force an engagement at Smolensk with the Russians and comprehensively defeated prince Bagration's troops ?
How probable would it be for Napoleon to be able force a peace on Russia, maybe pushing back the Russian western frontier to where it was before the Partitions of Poland and restoring to Warsaw the bulk of the PLC's lands ?
Napoleon did force an engagement at Smolensk (August 16 - 18, 1812 with a loss os 12 - 14,000 on each side) so there is no “if”. However,
Bagration was not in charge at Smolensk: he was commander of the 2nd Army, not of the whole Russian force and as formulated question does not make sense. Actually, at the evening of the August 16 he was sent to Valutino to cover Russian retreat: Barclays, who
was in charge, planned the battle as exclusively rearguard action.
To address your main question, Clausewitz wrote that advantage of the Russian position was in the fact that “
the battle could not result in a general defeat” and after losing Smolensk Barclay could continue the retreat. Out of 130K only 38K of the Russian troops had been engaged and the rest were on the right bank of the Dnieper: position at Smolensk was not good for a general battle.
Now, if by whatever reason the Russians did suffer the “comprehensive” defeat there (I’m not sure that even with Bagration in charge they’d manage to lose a half of their numbers) very little would change strategically. There are still the 3rd army and the Army of the Danube, the new troops are being raised and if Alexander did not make peace after losing Moscow why Smolensk would be more critical?
