What happens to the evacuees from Ft. Henry?

The English who are evacuated are slaughtered by the French and their Indian allies.

Actually, there was only one or two Frenchmen at that fight, and they were not wearing Royal French uniforms. The French were not going to help the Hurons because they had already made peace with the British for that day. The attack was instagated by Montcalm when he spoke with Magua in the forest, and this is all explained if you paid attention.