Personally, I would dump the "geography" of the True Afterlife presented in the book. Here's a cut & paste of something I posted on Monte's site:
To drift off-topic a bit, the answer to your question is:
* Monte and I were told the book would be 7 module units (MUs, each MU being 32 pages long). He would design four, I two, then he another.
* When we put a proposal together with a page breakdown, we forgot that extra MU at the end, and turned over a 6-MU proposal.
* Monte left WotC and the rearranged the schedule so I'd do 4 MUs and he'd do 2. When I saw that the proposal was originally for 7 MUs, RPG talked to the Brand team and was told that Brand received the 6 MU proposal and changed the product's spec sheet to reflect the "new" size (I guess the thinking was, "They say they can do it in 6 MUs, so we'll do it in 6 MUs").
* We finished designing Ghostwalk.
* A month later, Rich Baker (creative director for the project) asked me, "Was Ghostwalk originally 6 or 7 MUs?" I told him 7, which was changed to 6. He pointed at the sell-sheet, which apparently had _never_ been changed to 6! So this book had been written 6 MUs long, but had been solicited to distributors and retailers as a 7 MU book (and therefore at a certain price). Changing that now (5 months after the inital solicitation would be a real problem.
* So they took me off of another project (can't remember what right now, but it was something I wanted to work on) and had me write another MU for the book.
Monte and I had felt that leaving the True Afterlife mysterious and up to individual DMs was the best option, but Rich talked me into putting together what it might look like, since there would be some people who would want to know what the "official" version was. So I wrote 16 pages on that, and 16 on additional encounter sites within the Undercity since there weren't any of those in the book other than Monte's included big adventures (FYI, those sites are Kinship of Vermin, Lair of the Crippled One, Lair of the Eyeless Lady, and Morbid Maze).
So that's why the True Afterlife is the way it is: added at the last minute, and not in a way that we really wanted, but had to do.
With that in mind, I'd be more than happy to dump it as presented. If using GW with FR, I'd make the True Afterlife a subsection of the Fugue Plane, perhaps with some special rules, perhaps not.
Sean K Reynolds
Check out my two newest books, Anger of Angels
and Path of the Magi