I thing that while discussing what a Sarkozy or a Hollande win would mean for the EU you're missing one big thing about these elections: two politicians who built their campaigns on a platform to abolish the EU won 30% of the votes from those who bothered voting. Which does not include those too disillusioned to do so.
And this in the EU's most central country. And this before France entered a economic crisis that it is bound to enter this year. This EU is dead. All that's worth wondering about is what will be the the date of the funeral.
This EU is not dead. Not yet.
Almost everyone is convinced that the EU cannot continue in its current incarnation. That's why Hollande will probably push to add growth and pro-job provisions in the austerity treaty. If he can't manage to do it, European economies will be asphyxiated in months and then, yes, I suppose getting out the euro and seriously rethinking the EU will be necessary.
Now, what you are saying is rather inaccurate. First, I think even Ms. Le Pen doesn't specially plan to
abolish the EU and go back to the 19th century. She says she wants to get out of the Euro and indeed, the National Front's program is probably about considerably scaling down the European Union's scope. But every candidate has some ideas about the EU and most of them are about how to transform it to fit their ideas, not throwing it out of the window.
Second, the participation was 81%, which is among the highest for a presidential election in France. I'm fairly persuaded that most of the abstentionists are evenly distributed in the electorate. That doesn't mean that the 19% who didn't go to vote absolutely badly wants to see EU disappear out of thin air.
And third, I'm curious to know who is the second candidate wanting to abolish the EU. So far, the closest ones I see are Marine Le Pen (17,9%) and Nicolas Dupont-Aignan (1,79%), so, at best, you're south of 20%. That's almost surprisingly low given the fact that EU policy and directives are our politician's favourite scapegoats when it comes to justify their inability to get things done.