They HAVE to be saving it for Sargeras’ return. Imagine he returns and pulls the sword from the world. Somehow, they will make Sargeras a hero. He will help us. That’s why they jailed him and didn’t kill him.
We will see both Illidan and Sargeras again. Count on it.
Blizzard doesn’t do closure.
I thought the sword itself was the closure.
It’s a monument of our success against the burning legion, it’s just going to be part of the landscape now.
Maybe it can be converted to a place of pilgrimage.
I hereby award you the Necro Lord of the Day title. 
The sword is being setup as a Chekov’s gun. It will be the key to something down the road. The writers want you to forget about it.
Is. …is the sword Azeroth’s third leg?
The damage is not too bad. As long as the foundations are still strong, we can rebuild Silithus. It will become a quest hub haven for all.
Azeroth Explodes
Oof. Now those foundations are gone. Sorry.
…hic!