The term "Leader of the Landslide" meansthe leader of what bad things happened, like Junior Sparks' mom leaving. the lyrics "Is she dead? Is she fine? Every day, every night" are talking about how Junior wonders what happened to his mother. He thinks about it frequently. So basically, the theme of the song is Junior coming to realize that his dad, Jimmy, is the leader of everything that went downhill (landslide). All he really "wanted was a mother for the first time".