I don't think the IBF have decided whether they're going to allow Froch to keep the belt for this fight or strip him. They'll obviously get a massive sanctioning fee for Froch Kessler compared to Stevenson Whoever but why should Froch and Kessler pay them three or four percent or whatever it is? One belt is more than enough for this fight and the winner will almost certainly have to dump/will get stripped of one of the belts after they win it.