The aim of cutting off Napoleon and his army never existed except in the imaginations of a dozen people. It could not exist because it was senseless and unattainable.
The people had a single aim: to free their land from invasion. That aim was attained in the first place of itself, as the French ran away, and so it was only necessary not to stop their flight. Secondly it was attained by the guerrilla warfare which was destroying the French, and thirdly by the fact that a large Russian army was following the French, ready to use its strength in case their movement stopped.