I'd guess we will overwhelm Sargeras in 7.3 (Odyn-like), but there will be a major "plot twist" with Elune/Azeroth in 7.2 Tomb of Sargeras and the new dungeon, which will overall allow us to reason with the Dark Titan. After all, if Elune can be born, or if saving the galaxy from a Void Titan is just a matter of killing N'Zoth, Sargeras might want to take our side.