Medical treatment during the Napoleonic Era was very basic at best, mainly due to the limited knowledge. Sadly, the idea of the Humours was still a prevailing medical thought within the French military medical services. These medical services were also very new, starting under Napoleon and highly in demand as they were often attached to every battalion (cavalry would also have people knowledgable in horse care but not necessarily vets).

As a result, these surgeons would do whatever they could for anyone, interested in saving lives. This would extend to enemy soldiers if possible. However it must be noted that the medical procedures were very basic and a major battle like Borodino was long, many soldiers would have died before the day ended if their wounds were great.

However I must also point out that war at this time isn't as instantly deadly as contemporary war. A shot from a musket isn't necessarily deadly as there's a multitude amount of ways that the ball could be weak (from bad powder to distance and wind) and many people lived with being shot. Marshal Oudinot suffered over thirty six wounds in his life as a soldier, at least half before he was an important general (thus getting basic medical treatment). So in theory enemy soldiers could have just gotten pulled away by their fellow soldiers or walked back to the Russian camps.