When you enter Kuldahar you encounter a frightened townsperson, if you talk to him he will explain that he and his brother made a pilgrimage to the Vale of Shadows and only he returned. His brother and the family heirloom are missing.
I've completed The Vale of Shadows, The Temple of the Forgotten God and Dragons Eye each time I've taken just about everything from the various levels to sell off or equip. Everytime I visit this guy he keeps asking me if I've found it yet and I can only choose No and say that I'll keep looking.
Does anyone out there know what this heirloom is and where it is located - I only want to know if I've accidently passed it already in the levels I've completed. If I've yet to find it, let me know but don't hand over any more information than that.

Its been awhile, but I believe the heirloom was on the Yeti Chieften on the surface map of the Vale. He was at the entrance of the cave with the Yetis and the crates.

Yup. That's right. On the Yeti Chieftan outside that one cave.

Do you remember what item the Heirloom was? I've cleared the area and might have sold the thing in Kuldahar.

I think that it's either a gem or a necklace that the yeti was wearing. Sorry that I can't be more precise, but I went and saw him BEFORE I sold everything I had carried back from the Vale. Hope this helps.