It's highly hypothetical obviously. If Le Pen were to win, there'd be a significant chance that France would leave the EU. Should be considered that she is not some kind of Queen, there is still the legislative that could probably stop most of what she would try to do.
If Frexit happened though, I'd say a complete dissolution of the EU is actually quite unlikely. It would either just continue to exist as EU26 (i.e. current EU minus UK and France) or, in the very worst case, it would be a much smaller Union comprised of, say, the BeNeLux countries, Denmark, Germany, Sweden, Finland, and Ireland. I'm actually not seeing any real possibility that for example Spain would be like "Oh well, France left, so we'll leave too", and the same is true for many countries.
This is all highly unlikely, but IF France leaves the EU, Schengen would look weird with this big hole between Germany and Spain...
If France goes out under Le Pen though it seems they are putting themselves in a weird position if they don't include themselves in another Franco-German (with Benelux as binding middle partner) coalition.
I'd love to see how she spins this. Because yes, France is fucked witrhout some kind ogf union, most obviously with Germany.
I wouldn't love to see that enough for wanting Le Pen to win though.
France deserves every bit of credit for what it did in WWI
IMO, no one deserves any credit for WWI. God, what a waste.