I don't think he's locked in. If Taylor and Kessler could pull out (even though it was due to injury) than I'd think any of them could pull out. Also, Abraham-Froch was supposed to be in Germany originally, not England. And Dirrell definitely wouldn't be willing to go back to England to fight, not after the bull**** that happened last time. I think he even said on Fightcamp 360 after the Froch fight that he would never fight there again.
Forthe record, Green would have to KO Johnson AND Dirrell would have to lose to make those four the guys.