I had a CTD entering the third Khan supply cave near Bitter Springs, only my second, and now multiple parts of the world are missing that were there before. The main one occurs around the top of bitter springs where you get the two quests. As soon as you approach the tents both the quest fail as the quest giver has fallen through the world to her death.

I went back to saves hours before this happened and I still have the problem, I even went back to a save before I even found Bitter springs and fell through the world somewhere else that worked fine before. I tried reinstalling the game and nothing has changed. So are all my savegames stuffed or is there someway to reset the world, some sort of cache file that the reinstallation didn't touch?

I downloaded all the patches.

Deleting the two config files in the user data folder fixed it. 35 hours not down the drain thankfully!