According to this article in Le Monde, yes. Ministers leaving the government, such as Cécile Duflot, can reclaim their seats from their suppléants. And Duflot, who is leaving because she vehemently disagrees with Valls on the Roma issue, need not vote for the government. The Front de Gauche has already said, in the person of Mélenchon, that it will not support Valls in a vote of confidence. And the absolute majority hangs on only 2 votes.