Here is a slightly different 1940 scenario in comparison to our TL:
Let's say that, rather than sending his strategic reserve to the Low Countries, French General Maurice Gamelin initially keeps his strategic reserve at Rheims (as per the original plan). However, let's also say that the Nazis realize that the location of the French strategic reserve is a serious danger for them and thus decide to invade Switzerland in order to get Gamelin to move the French strategic reserve over there and away from the Ardennes (for the record, I think that Joseph Goebbels actually proposed something like this in May 1940 in our TL). Gamelin falls for this trap and begins moving his strategic reserve to Switzerland while the main German assault still occurs through the Ardennes.
Anyway, what happens in this TL is that the French and British forces in the Low Countries still get cut off by the Germans as per the Manstein Plan. However, what is different in this TL is that France still has a strategic reserve which has been moving towards the Swiss border (since Gamelin didn't know where exactly the main German attack would be and thus decided to send his strategic reserve to Switzerland to help the Swiss fight the Nazis there).
Basically, my questions here are these:
1. Can the French strategic reserve get back north in time and successfully break the German encirclement of the French and British forces in the Low Countries?
2. How does the Battle of France progress from this point onward?