That's why I hope Larian is cooking a DLC and the theme will be Avernus, it makes sense Avernus to be the zone. On one hand we can continue Karlach story, on the other if Wyll still has his pact, we can try to pursue and convince/kill Zariel. Especially that BG3 happens after "Descend into Avernus" book, there are 9 layers we can see!