Who knows, but the plan itself was sound and it worked. It forced Germany to go via small route and thus made much less land that needed to be defended. They just didn't have a plan to defend that land - if they had a workable plan Germany would have been in real trouble - their troops were overextended on hindsight. It worked because France was incompetent not because Germany had a great battle plan.
Indeed, I believe the initial plan was to continue the line, but Belgium opposed it. And the Ardennes was thought to be difficult enough terrain that it didn't need to be strongly defended. It was actually the Ardennes that failed expectations as defensive terrain, not the Maginot line (though as you noted, it would have worked as defensible terrain if there was more competent leadership).
It's kind of like building a giant fence around an area, then leaving an opening in the middle of it, and then deciding that you don't need to have people guard that opening. And when people inevitably get through the large unguarded opening, you declare that fences are idiotic and useless.
The issue was that while Ardenne were a bad train to fight in, the French didn't contest the German advance there with fool reasons, so they kinda just traveled trough it. Hard terrain isn't that hard if undefended.
Continuing the line was an impossibility because it would have driven the low countries straight into aligning with the Axis.
Just because political concerns ruin your tactic, doesn't mean those political concerns aren't real. The Maginot line was great tactically, but worse than useless strategically, because it completely failed to achieve it's big-picture objective - keeping the Germans out of France.
The low countries were against it because they feared the Axis, and didn't want to be left on the other side of defensive fortifications. But in the end they fell to the Axis anyway, so I'm not sure how not continuing the long helped.
Either way it's a moot point. As I said, the Ardennes would have been an effective barrier if it was better defended. You can't leave an unguarded opening in your fence and then declare that fences are useless.
Yes, France still fell in the end. Static defenses weren't able to overcome weak leadership, but - importantly - it's mobile forces weren't able to overcome it either. In the end the mobile forces ended up being _much_ more susceptible to poor leadership than the static defenses, leading to a large chunk of the army getting disastrously cut off (and the need to get evacuated from Dunkirk).
For a little bit, anyway. But what does that actually mean? I often wonder what would have happened had Germany not pursued genocide, and just stopped at France. It's not like the French people would magically turn German overnight. Would the resulting entity end up like a confederacy?
Same reasoning with Napoleon, too. What if they had stopped before the Russia disaster?
Poland has treaties with France and England: both were in process of mobilizing after the fall of Poland. I think it is inevitable that England would have at least made some attempt at war.
Though I wonder if Hitler could have made things worth if he had not started the Eastern front. (I'm not clear on how that started, and Stalin wasn't to be trusted)
