On reading this thread, I immediately thought of faery.

It has contradictory associations with lands of the dead, the etheric plane and overflowing life, an alien landscape, and the idea that it's somehow fading away without ever disappearing. There's also that strange business about the "tithe to Hell", which could imply souls beyond the normal recarnation cycle periodically get punked into incarnation.

Who knows, maybe magic has decreased in material efficacy because they're using it all in preparation for their departure.