I like to complete/explore all the details possible of all the maps, and today in Vana's Reach, the map exit just south of Trupo's Outpost, I think I discovered a bug in doing so.
When you get to the shaded area and it asks you if you are ready to leave the area, select "no" and keep going to the edge of the map. If you click back and forth at the very edges, and get someone to walk off-map, they disappear, and then if you wait until the next "are you ready" dialogue and click yes this time, doing so while they are off map, they will be permanently gone. This happened to Khalida in my case. I went back to the hand camp, the hands dispersed, I left the area, chose Khalida, and she was still "not there". She showed up as being a party member, but was simply not there.
I had to load a save from before I did that to get Khalida back.