Hmmm... the tsar would have 3 options.
1 Give up Modern Day Ukraine and hope Napoleon comes into modern day Russia. Even if Napoleon keeps his losses to 25% instead of 75%, if Napoleon goes into Russia the winter will
Or just give up Ukraine and wait for Napoleon to go elsewhere. The whole GA can't just sit in Vitebsk for ever. As soon as it moves elsewhere, the Russians move back in, and shoot or hang any Polish magnates there who have collaborated with the French. Given Russia's all but unlimited manpower, even the worst battle losses can be replaced before long, so this is feasible.
Indeed, even while the GA is stil in Vitebsk, this could be done in places not too close to that town. Also have the Cossacks lay waste the surrounding countryside, and kill or capture any foraging parties.