If Macron does win in the second round, which he most likely will outside of a nightmare scenario, then I think that's setting up an even bigger disaster down the line. When you boil it down, he's really a continuation of Hollande's neoliberal policies, and his main selling point is this cultural liberalism that I think can only get people excited for so long.
Base point, people don't like neoliberal economics. And if Macron is really going to tear down the labor unions and govern as a pro-business centrist, I have no doubt there's going to be another Le Pen that comes down the line who's able to better sell right-wing populism to people, and outright win.
You think it can't happen there in France? We didn't think it would happen in the US, and we ended up with Trump after the path was set down by the Clintons in the 1990s for a truly terrifying kind of conservatism with the Republican Revolution of 1994. Buckle up.
Macron is a man without a party, though. If Macron fails, there's plenty of room for the PS, or another left-wing alternative, to come roaring back without having to take the blame for his failures. I think what his impending victory shows the most is that there is no nationwide victory available for the FN in France, period, with the sole exception if they are lucky enough to end up in a runoff with a fatally crippled traditional right-wing candidate where the center and left stay home (though even Fillon would likely have won a runoff against Le Pen). The left-wing and centrist vote will keep reorganizing itself in different forms to block the FN at every turn, and the remaining traditional right-wing vote is not the type that is sympathetic to the FN's cause.
The French left can't incompetently govern forever just because of FN.
