A lot of systems are now getting automated via player vs AI mechanics.
1. A new version of a battleground where you fight as a team of players vs an AI team is coming.
2. Followers are supposed to become super important in 8.2 per Taliesin's newest video.
I expect as the playerbase shrinks to nothing, they will add AI tanks, AI healers, and AI DPS to dungeon parties and raids to fill the gaps and keep the queues popping. We might end up with effectively solo dungeons, with 1 actual player and 4 AI. That will be the final version of WoW at its sunset, with very few players but technically you can run anything because AI will be there to make a full and complete instance. Maybe they will even add AI to the auction house so mats and stuff are available to buy.
The game will play itself.