It was recently announced the the title of the final book will be United as One. It did confirm my hunch that it will focus on the numeric "one," not referring to number One caught in Malaysia... And it did also confirm my assumption that the title would break the four-word pattern...
Check out the cover of United as One by Pittacus Lore.
The official synopsis is still in the wrap, so no luck of knowing this early what will our fate be after the cataclysmic battle.
United as One by Pittacus Lore will be released on June 28, 2016.