Just a few years ago, underemployed TV writers were complaining that reality programming was taking over their industry. Now the scribes are having their revenge: Unscripted programming is mired in an unexpected slump. Onetime smashes such as "Survivor" and "Dancing With the Stars" are drooping with age. Coca-Cola recently wrapped up its 13-year sponsorship of "American Idol" after Fox's singing hit plummeted in the ratings last season. NBC's own singing show, "The Voice," saw its season finale drop nearly 10% this month. And what's worse, no new hits are taking their place.