Complex sentence: Barda's condition worsens, until he has almost died when all seven tribes are reunited and Lief realizes that Dain is the heir as the belt is showing that the heir is somewhere in the room and that Dain's name is an anagram of'Adin'.
Split into simpler sentences: Barda's condition worsens, until he has almost died when all seven tribes are reunited. To help proove this, Lief realized that Dain's name is an anagram of'Adin'.