Ted Koppel hangs up his cleats at ABC tonight. But in an interview with Charlie Rose last night he hinted that he will be returning shortly to the airwaves, perhaps at HBO. Koppel prides himself on mature truth-telling, so he had no problem telling Rose that ABC gingerly showed him the door because his salary was going up and his ratings were going down. ABC wanted to throw a hail mary and expand the show to a live hour -- Koppel disclosed the trade secret that the beginning of the end for a show is the moment when executives start talking about expanding it -- but Koppel didn't want the bother and didn't want to have hang around ABC until midnight.