Whatever they deem necessary? People really have no idea what a just war is anymore do they?
I'm not French, so I don't give a fuck what they do, but assuming the terrorists didn't attack first, which they didn't, then there is no justifiable reason for France to have troops over there. They are the aggressor. Now, if that's what the government wants to do and the people want to do, then this shit will happen. War isn't nice. It is miserable and despicable things happen to both sides. You would hope they would stop fighting so no more innocents die. They won't though.