Okay, so it's only 1 week until Antorus opens, so some last minute speculation!
Yes, we know the Pantheon will imprison Sargeras in the Seat of Pantheon, and Illidan will be his jailer, but how?
Will it be...
1. Pantheon imprisons Sargeras's physical body inside the Seat of Pantheon. Illidan, powered up by the other Titans, will duel Sargeras to the end of time to prevent him from escaping.
2. Pantheon imprisons Sargeras's spirit inside the broken body of Argus. Illidan will be watching over the prison, similar to how Maiev watches over his.
3. Pantheon imprisons Sargeras's spirit inside Illidan, Tal Rasha style. Illidan has to fight the influence of Sargeras as he stays inside the prison.
4. ???
How do you think this expansion will end? How will the biggest threat to Azeroth face his defeat?