: Except that the Trow aren't part of Wyrd's creation. Why
: would they return to the One Dream on death? Or is
: Acerus Malum Magnus just patronising the kid?
Random poetic interpretation--if Wyrd's One Dream is the world, then Nyx appropriated chunks of it when she molded the Trow from the ground and infused them with spirit. When they die and revert to rock and clay, their bodies are becoming part of the world--the One Dream--again.
Alternatively, the One Dream may be a more fundamental layer of reality from which the Trow believe their souls come.