I assumed I would see him in the Great Khan camp, but he's no where to be found after siding with him and getting him accepted by Papa Khan. I even ran between the two locations looking for a body several times, but still came up empty.

Is this a bug, or has anyone else been able to find him after completing the vault 19 guests?

Thanks!

Its not bug they just never wrote in the follow up for having them hook up with the khans.

he never shows up but at the ending it tells how some made it in to the khans and others were not due to the trials they had to do to prove them selfs worthy

You don't see him in game again. He seems to be tough enough to survive getting jumped in so he shares whatever fate you created for the Khans in the ending. For reasons good or ill, he won't trouble the Mojave again.