Well, that depends. Do I still have to end up at the same place as BFA? Where Sylvanas is the enemy of all life, leading into Shadowlands? Because if so, that kinda handcuffs things.
If not, then I just would have told a story about a battle between the Horde and Alliance and the attempt to control Azerite and heal Azeroth.
The Alliance would have attacked Undercity first, because Sylvanas has given the Alliance more than enough reason over the years to get rid of her. And in response to losing Undercity, she would have attacked Teldrassil, which would have been burnt down by a malfunctioning Azerite superweapon.
At this point, expansion starts off the same. Alliance and Horde recruiting the Kul Tirans and Zandalari to their causes. Warfronts at Arathi and Darkshore. Raids in Uldir and Crucible of Storms.
7.1 Warfronts in Gilneas and Mount Hyjal as the Horde and Alliance take more and more enemy territory. Battle for Dazar’alor raid happens. Kul Tirans and Zandalari join the Alliance and Horde.
7.2 Dual expansion areas of Mechagon and Kezan open up as Alliance and Horde search for more weapons/allies/resources. New Warfronts at Silvermoon and Exodar.
7.3 Exodar and Silvermoon have both been lost to their respective factions. Each faction has now solidified it’s control of one of the major continents. At this point, the “Azeroth is dying” issue comes to a head, and both sides have to stop fighting in order to deal with it, with a raid that involves delving deep into Azeroth to try and find a way to remove Sargeras’ sword and heal the wound.
All of the Nazjatar and Ny’Alotha stuff would have been saved for it’s own expansion.