I know that this is necroing but the thread has good ideas that I wanted to add to. Our DM was quite disappointed by the fact that the first 3 books were not set in the country so what he's doing is having us play through the country before the fall. He looked at the state of the country in the later books and has built the early adventure off of how he thinks the situation could have led to that. Naturally this means the potential of a fair bit of rewriting later depending on how the PCs may influence the "past" of the AP. We're currently doing the ruby phoenix tournament as a means to earn our way back to the living world after traveling the underworld for an equivalent of 25 living years as a time skip but we've gotten glimpses of what our past actions enabled for the present compared to what he revealed about the original book.