I trust Snyder. I am just not sure what the devastating event will be. Can't really be the death of Robin/Hood/Batgirl/Nightwing/Tim. They all have their own books basically. Alfred's death would be devastating but not sure if that is where Snyder wants to go. I feel like it has to be something that tears the Bat family apart. Joker's point is to separate Batman from those that make him weak. Just killing one of them wouldn't really accomplish that goal.
Also, I hope that nothing game changing happens with Harper. She really isn't doing anything for me. If she some how get a bigger role in the bat family after this I am not gonna like it.