I just finished reading Nagash the Unbroken, and while in general I loath warhammer Fantasy, the Time of Legends books have been great reading. Furthermore, the one aspect of Fantasy I love is Nagash's storyline. I think if Nagash returned to Fantasy, I would as well. But, I fear he has been resigned to the old days of herohammer.
So Nagash the Unbroken is written by MIke Lee of Mallus Darkblade fame. He's a great writer, and I would love to see him venture into 40k territory. If you have read the first Nagash book, then definitely read this one. If you haven't read either, than definitely do so. This book covers the period where Nagash is wandering the shores of the bitter sea and the simultaneous events in Lahmia.