...that one of his family members has to die. For the entire series, Skyler has been telling Walter, "You can't do this, it's going to put our family in danger." There has to be a pay-off.

I think it's going to be Walter Jr. It goes pear-shaped with the Czechs and they call in the goon squad to get Walt back in line. Probably those shit-crazy skinheads in the last half season finale or the exterminator crew. Maybe some home invasion shit. That leads to Skyler fleeing with the kids and the house being abandoned.