Le Pen is definitely running, has announced the fact. He may be expected to get at least the 16%-17% he got last time, and quite possibly more. In the first round, that will be votes Sarko will not get. Polls indicate that Sarko will all the same clear 30% in the first round, and therefore get into the second. (Though at this stage, this is not sure -- polls always show a low estimate for the Le Pen vote, possibly because some voters don't want to admit to voting Front National).
Sarko's "work" on law 'n' order 'n' immigration themes was designed to chip away at Le Pen's base. And get that base behind him in the second round. He may succeed in getting more Le Pen voters behind him in Round Two than have previous "centre-right" candidates in presidentials, but his problem now is that he's positioned way off to the right and has left open an avenue, un boulevard, in the cantre. Which Royal and François Bayrou are benefitting from, and Villepin and Alliot-Marie are ogling with appetite.
Chevènement (sovereignist ie anti-EU left) has announced his candidature again but said he will desist if there appears to be a risk of a Sarko-Le Pen second round. It doesn't seem likely the Radicaux de Gauche will field a candidate (pity in fact, since their candidate, Christiane Taubira, is a black woman and has plenty to say and says it well). The non-PS left is wallowing around in a mess and currently polling weakly. (Pity again, since the Greens are almost disappearing in this mess).
The remaining query is: will Fabius be tempted to run a rogue candidacy? He got 18% in this primary. He's not considered credible by the hard left. He doesn't appear to have a base there on which to run. If he does, it will be a vanity thing. Would he succeed in splitting the vote? Possibly, but he might get a backlash against him.
P.S. When I was young law student in N.Y. in the early 60's I worked for the Reform Dems to oust Carmine DeSapio. We won and got Ed Koch. I regretted that my whole life. Hey, Grandma Moses started late!
She won, she really won, and everyone will be behind her now.
AFAIK, Fabius has not yet spoken but is expected to do so soon.
He said it was now up to Royal to bring together the socialists, and he was personally prepared for that. He let it be understood, however, that he expected her to take his more leftish policy planks on board... With, I suppose, the threat behind that of not calling to vote for her come the election.
