Watched the cinematic a few times, I noticed that Argus, in his world-soul form is floating in the center of the Seat of the Pantheon.
I imagine we didn't kill him as much as we freed him from corruption and returned him to his primordial state to develop free from the influence of Sargeras. Which means if and when the pantheon returns, it's likely an uncorrupted Argus will be among them.
If I were to speculate further, I imagine we'll see all the titans battle the Void Lords in some future expansion. Nine titans with Azeroth. Or eight versus Azeroth. Who knows?