I had this idea since last night, even if Luffy crash the wedding and take Sanji successfully, the Germa and the big mum crew still have a card up their hands, and that is Zeff's life.
They could possibly say something like "Once you take a step off this island, I'll make sure that man die a bloody death". Which means Luffy have to trash either Judge or Big mum herself to end the threat.
What do you guys think? tell me in the comments.