Then it's also possible he got killed by some wildlife, since he likes to run up to you no matter what is going on around you at the time. I had him actually start talking to me during the powder ganger attack at Goodsprings during one playthrough.
He also likes to get himself killed in Primm on the new traps that I added in my mod...
I took pity on him and added a journal to his inventory that explains what he'd tell the player if he was still alive.