This is what I found for you at: http://www.eyeonsoaps.com/AMC/trivia.htm
**Let’s clear up the Bobby Martin problem once and for all: Bobby, played (albeit briefly) by Mike Bersell, did not go upstairs to polish his skis, never to be seen again. He in fact went off to summer camp, where he apparently slipped everyone’s mind forever after. Almost twenty years later, the writers did get a little comedy mileage out of the situation, though: Opal Purdy, who was staying with the Martins for a while, accidentally got locked in the attic. While rooting around up there, she stumbled over a skeleton sitting next to a pair of skis, on its head a baseball cap with the name Bobby on it.