A convicted sex offender whose name and mug shots appear on the statewide most-wanted list of probation violators has been dead since 2002, officials discovered this week. Robert Sieracki failed to appear at a probation hearing, and had warrants in Barnstable District Court and Barnstable Superior Court for indecent assault and battery on a child, said Coria Holland director of communications for the state Probation Service. Sieracki also violated the terms of his probation in 1990, said Dave Procopio, State Police spokesman. “He was not supposed to be alone with children,’’ Procopio said.