It's been 4 days. Claudia went out this morning to look around, and never came back. Then Mr. Cob went out to look for her, and HE never came back.”— Carrie Delaney
After the bombs fell, Cob and a few others ventured out into the wastes to search for help, never to return. It is not made clear whether he was a Teacher or one of the parent-chaperones.
Cob is mentioned only in Fallout 3.