What time is it? He might be inside one of the buildings. Look up and down the road, sometimes he runs from me when I approach him too fast.
This is from the wiki:
http://fallout.wikia.com/wiki/Chomps_Lewis
On some occasions after clearing the quarry of Deathclaws, it has been known that in the afternoon to night a random Deathclaw runs straight for Chomps Lewis from the opposite side of the buildings at Sloan and immediately attacks him, most times killing him. It is challenging trying to prevent his death so that you can get the reward and not failing the other quest "Don't Make a Beggar of Me". If you are patient you can wait for the Deathclaw to come out, Or you may quickly collect the reward and then leave him to his fate.
This must be some kind of bug or something. What is the purpose of making a NPC you can get a quest from if when you complete the quest you can't even find the guy to move the story forward and get a reward and another quest from the dude... It is a bunch of nonsense. Really frustrating that I cannot find the guy all of the sudden and get the money and experience points for completing such a hard quest killing an entire family of deathclaws. Especially that Alpha Male, he was tough. Killing the mother did not prove to be too difficult as she was stuck and made for an easy sniper target...
Just wanna find the guy and get mah loot...