I think some of that is getting pushed off a bit. We’ve got these D’Orc squads closing in on various Dooms, so I think that, and battles surrounding them maybe eat up a lot of time. Also, it may take the Storm Lords [i]a bit longer[/i] to get back to Necropolis than they expected.
[SPOILER]As Exador tells them early on in book IV “what did you expect? You have to prepare both departure and destination points. We left in a hurry, remember how this was a foolproof plane? How many places do you think I have prepared where it will be night and your army not get barbecued?”
So they are not exactly somewhere convenient, and their army is in a really bad state after having gone through the Abyss, and are probably not going to want to do another switch anytime soon.[/SPOILER]