That would be true if they didn't have their own electorate to question to.
If France leaves we'll see a massive financial crisis and a massive build up of arms all over europe. Basically go back to 1925.
The give me something or i'll leave approach will backfire just as it did for the UK. Only that it's not gonna be one country fucked but all of europe(and probably the world).
I agree that the EU needs to be reformed however threatening to kill yourself if it doesn't happen is just childish.
We should rather try and get countries on board for reforms (if necessary go a multiple speed europe like proposed) and leave the unwilling obstructionists behind.
France vs. the EU, and we just escaped the depths of the crisis. Fun. It's not really a "democratic refounding" if France takes its ball and goes home.
I think multi-speed Europe is a decent idea, but will not get much support in home countries. It's easy to just blame the EU for the failings of national governments.