magua talking to montcalm

That's a fair point.
However, Montcalm surely realised there was an extreme risk Magua and his war party would attack the Brits leaving the fort.
Having said that, they seemed unprepared and it was out of character for Munro not to have sent out scouts. He was such a diligent Officer of the Crown otherwise.

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In the Director's Cut, when Montcalm goes to talk to Magua after the fort surrenders, there's a small change in the dialogue. In the theatrical version when Magua asks Montcalm if he thinks the English will honor the terms of the agreement, Montcalm says Colonel Munro would but General Webb won't. In the Director's Cut, that line isn't there.
My DVD is called "Director's Expanded Edition" and it is in there. It is an important scene and should always be present. Montcalm had up to that point been shown as an honorable and humane man. This scene shows him to be devious. From their facial expressions, not just the dialogue, it is clear that Montcalm is giving Magua licence to massacre the departing British while himself adhering to the letter, but not the spirit, of his promise to Munro. His justification to himself would have been his assumption, probably correct, that Webb would similarly renege on the deal.

There is not a lot of subtlety in this movie, good as it is, but this is one scene that does add another layer.

It is a shame they messed around with the editing and different versions. A fuller version would have been more satisfying. The relationship of Uncas and Alice needed more scenes, for example.

What London777 says is true: I just saw the Director's Expanded Edition and the line is there: Montcalm says that Munro would honor the terms of the surrender, but Webb wouldn't; and so Montcalm & his troops would eventually face the same soldiers again.

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