The ones captured by Ogres in TBC kept saying that a "hero would rise" in TBC. I assumed they were just talking about the player-character.
In hindsight, the writers were probably talking about Garrosh.
Uh, nothing? They had no idea he would turn to diamonds. How do they reverse it?
Ashenvale. He has a grave site and everything, though the Burning Legion has claimed it because it's where Mannoroth fell.
Training more Argent Crusade members.
You can't hit radiation with a sword and expect favourable results.
If heirlooms are any indication, those weapons get sold to young adventurers.