Steve D (putting his ass on the line here with this suggestion, but...)
FPW has already written in stone that there will be no sequel to Nightworld a la MAD MAX and no prequel to The Keep; however, what if DEMONSONG were one of many encounters by Rasalom and Glaaken in post-destruction worlds reduced to barbaric post-civilizations by Rasalom? Wouldn't that mean that in yet another post-destruction world (namely, Earth) after Nightworld that Rasalom and Glaaken could meet again in the barbaric post-civilization that would grow after Nightworld on Earth? The Keep prequel (which would be in flashback to their real first meeting) and the Nightworld sequel (which would be in the present at their real final meeting, leaving Jack and family and the other survivors representing the new world ahead after the grand battle and thus closure) could be wrapped up in one book: The real grand finale of the Adversary Cycle in the post-apocalyptic world of Nightworld.
Anyway, this is what I dreamt last night after eating some Thai food, so you can imagine how I spaced-out I must feel right now, waking up with this idea in my head. It made so much sense in the dream. Jack was there. And Glaaken. And even you Toto. Sighhhhh. Ah, but a man's grasp should exceed his reach, or what is a Heaven for? Alright, I'll go take a Zantac now. I'm sure there is nothing here that Mr. F Paul Wilson hasn't thought of already....
THE END??????