One idea that I came up with make work on how they survive. Someone (probably the master) keeps the bomb from going off and after listening to Elfman's explanation to everything (if they get one out of him), they realize they can't rush at it like they used to, especially since Tartarus has hostages. So to keep the element of surprise, they all discretely leave the guildhall and then allow the bomb to blow it up. Everybody lives and they get an edge on the demons. I know it sounds unlikely considering this is Fairy Tail, but it could be a way for them to turn this mess around. What do you guys think?