I have a simple fix. Kill Deathwing via quests with the help of Alexstrasza, let him die. But then at the end, the twist, you think "wtf this is tsupid" etc etc all the way through, you play off against an old god or w/e at the end.
Then in near defeat of the old god after a massive difficult lengthy battle, the god erupts and bursts and out through a maelstrom of blood comes Deathwing, the Undying. (He pwnt Nax). To give you another fight making the end raid an epic gear check and wonderful twist you only learn after doing the final fight on heroic or something.