Tufte points out that a large fraction of the losses occurred before the really bad weather set in. I also wonder how far there was an "original plan". Napoleon may have expected Alexander to ask for terms well before he captured Moscow; or he may have imagined wintering in Smolensk or marching on St. Petersburg.
- the Grande Armee was walking from Paris to Moscow, and quartering in the field along the way.
- the army was fed (as routine for all pre-railway armies) by local looting.
- the Russian response to this was to burn everything in the path of the advancing army that they might capture or make use of. This rendered the original plan to spend the winter in Moscow impossible.
A large fraction of the army starved, as was to happen later to the German 6th Army at Stalingrad. Or froze due to lack of available fuel. Or slipped away in the night to forage and never came back.