Wrong forum. But anyway:
The German Army would have moved elsewhere, and the French could have done one out of these things:
a) Retreated to Paris
b) Pushed further toward Germany
c) Attempted to follow them
B is unlikely because it would have left them too badly defended.
In the case of C, France would have stayed to the West while Germany, on the Eastern side of the front, would have moved South first but then gradually made a curve, pushing the French North, giving them no hindrance to reach Paris. The French would probably realise the inevitably of this beforehand, so this is equally unlikely.
Leaves us with A.
My point: The retreat to Paris was rather necessary.