NBC says ”30 Rock” will be returning next season for a final, abbreviated run. The network said Thursday the much-acclaimed sitcom will air 13 episodes in its seventh season before calling it quits.      The show has been a critical favorite since premiering in 2006. It has won numerous awards, as have its creator-star Tina Fey and co-star Alec Baldwin. Many high-profile guest stars, including Matt Damon, Elizabeth Banks and Al Gore, have appeared on the show.But the series was never a ratings smash, and this year its audience has dwindled to an average 3.5 million viewers. NBC will join other broadcast networks in unveiling full new prime-time schedules for advertisers next week. NBC will make its upcoming lineup official on Sunday.