This may only be tangentally related, so I apologize if this seems to threadjack.
I started a 1st level game several months ago with my players in the Greyhawk setting. The Big Bad Evil Guy (behind the scenes) was looking for a component to complete an artifact that opened a rift between Greyhawk & Ravenloft, and basically allowed Ravenloft to 'merge' with GH. The players found the artifact in the first adventure, and (insert long story here) ended up being captured & killed by the Bad Guy.
So I had them create new PCs. I started the new adventurers in a new land, with a higher level of technology and a heavy French influence (Dementlieu). I never told the players that they were in the same world, 300 years into the future, after the corruptive influence of Ravenloft had warped the land of Greyhawk, merged and re-formed it into an abominable combination of the two settings.
Some of the names of 'good' gods of the setting are variations or corruptions of the names of bad guys they faced originally, and likewise the 'evil' gods are corruptions of original player characters' names. There are legends of the evil 'party of adventurers that ruined it all' (i.e. the players' original characters). I've also been dropping hints as to what happened here and there, such as journals explaining that "the world ended 300 years ago" and things of that nature.
So now the City of Greyhawk is Dementlieu, Dyvers is Mordent, etc etc (I wasn't trying to make an exact recreation, I just slapped names on places as I liked.)
One of the last adventures we were doing in Greyhawk was Goodman Games' Idylls of the Rat King. I can't wait for the players to stumble across the one dusty little ghost town that didn't get renamed....and they'll see a crumbling manor house with the name Gannou on the rusting wrought-iron fence. The players will flip out, even if the characters have no clue....