It is 100% implied he HAS to stay wherever we leave him. You're the one that can't seem to use logic.
Voice of Amanthul: We will use the last glimmer of Argus's power to bind him here. The Seat of the Pantheon shall become Sargeras's prison... and ours as well.
Prophet Velen: You would condemn yourselves to stop him?
Illidan Stormrage: Our world must survive... no matter the cost!
Voice of Amanthul: A sacrifice must be made.
Voice of Amanthul: Return home, children of Azeroth. Protect the final titan.
High Exarch Turalyon: Prophet... what happened out there?
Prophet Velen: Illidan serves as the Dark Titan's jailer. His sacrifice has ended the Legion. At long last, the Burning Crusade...is over.
Sacrifice implies he stays there and it is obvious we leave from wherever there is and he stayed and must. Just stop talking before you make yourself look more foolish.