After firing Charlie Sheen, CBS is looking to cast a new actor for its cash-cow comedy "Two and a Half Men." Critics wonder if the show can go on without Sheen, but television history is peppered with programs that have lost marquee names and continued, successfully or otherwise. Here, ten shows that lived on after losing a top star:

1. "Bewitched" (1964-1972)
Dick York played Darrin Stephens, a mortal married to a witch, on the beloved ABC sitcom from 1964 until 1969. He had to quit due to a back injury he suffered during a film shoot years earlier, and producers quickly hired Dick Sargent to play the same role. The show continued for three more seasons, albeit with lower ratings. This is the "most famous TV switch" of all time, says Walt Belcher at The Tampa Tribune. But audiences these days are more sophisticated, says Alex Strachan at, and "no one will accept another actor in the exact same role."

2. "Happy Days" (1974-1984)
Ron Howard left after seven seasons, and Ted McGinley joined The Fonz's extended television family as a cousin of Howard's character. Even so, producers decided to shift focus and play up "the inexplicably but genuinely popular Scott Baio," says Jaime Weinman at Maclean's. With Baio's character, Chachi Arcola, adding new verve, ratings "actually went up" after Howard's departure. It just goes to show that a sitcom can "re-group and re-tool" if it has someone else it can "elevate to stardom."

3. "Charlie's Angels" (1976-1981)
Farrah Fawcett-Majors "was television's biggest new star" when she left the show after just one season, says David Bauder of The Associated Press. Cheryl Ladd "parachuted in" to play the sister of Fawcett's Jill Munroe, and despite the "almost impossible task," she won over the show's fans, says Strachan. The switch worked because Ladd brought a "new, youthful vibe" and didn't really try to copy Fawcett.

4. "Cheers" (1982-1993)
Shelley Long won an Emmy and two Golden Globes for her role as waitress Diane Chambers, and her decision to leave the show in 1987 "was probably one of the greatest career stumbles in show-business history," says TIME. Kirstie Alley joined, and the hit show went on for six more seasons — "one of the few instances in which the show actually lasted longer" with the replacement actor, says Bradford Evans at Splitsider. Instead of being mainly about "Sam and Diane," the series with Alley relied more on its entire ensemble.

5. "Valerie" (1986-1991)
This family sitcom was built around star Valerie Harper, playing a mother of three kids, but by the second season "the focus had begun to shift to the younger cast members, notably Jason Bateman," says Rob Salem at the Toronto Star. An unhappy Harper was "summarily dismissed" and her character was killed off in a car accident. "Valerie" without its Valerie "was really a stretch," says Robert Bianco at USA Today. The show was eventually renamed "The Hogan Family," and even switched from NBC to CBS.

6. "Law & Order" (1990-2010)
The long-running NBC drama became famous for its repeated cast replacements, but an early change may have set the stage for its extended success. After 88 episodes as the high-minded lawyer Ben Stone, Michael Moriarty left the show in 1994, because of political differences with producers. Sam Waterston signed on for the fifth season, and the legal drama became "a very different show, as a result," says Strachan. The program may have been a "more thoughtful, cerebral series" early on — but it did end up tying "Gunsmoke" as television's longest-running primetime drama.

7. "NYPD Blue" (1993-2005)
"Memo to any actor who thinks his hit show couldn't possibly go on without him: Yes it can," says TV Guide, and David Caruso's flame-out proves it. When Caruso didn't get a "major salary increase" after his first season on the show, he gave up his badge and gun to pursue a film career. Jimmy Smits came aboard for five seasons, and "NYPD Blue" lasted 12 seasons in all.

8. "Spin City" (1996-2002)
Michael J. Fox revealed he had Parkinson's disease in 1998, during the show's third season. Fox stayed on through the end of the fourth season and then producers brought in Charlie Sheen — yes, the "rock star from Mars" himself — for two more years. The revamped show "was still very watchable," says Bradford Evans at Splitsider, but "it just wasn't the same."

9. "CSI: Crime Scene Investigation" (2000-)
Lead actor William Petersen was "arguably the one true star in a well-oiled ensemble cast" when he left the hit show after nine seasons, says Strachan. Producers lured a bigger name, Laurence Fishburne, as a replacement, but the actor "has had a hard time fitting in," and ratings are slowly dropping.

10. "American Idol" (2002- )
Caustic judge Simon Cowell left television's most popular program at the end of its ninth season to work on a rival singing competition, "The X Factor." Aerosmith's Steven Tyler replaced Cowell, and Jennifer Lopez also signed on as a judge. Despite "an offseason of predictions that the ratings juggernaut was on its last legs," the viewership has held steady and the "re-energized" show "may have found its new Dream Team," says Brian Mansfield at USA Today. Even Cowell himself approves of the changes. "I personally think it is a better show than last year," Cowell says, as quoted by CNN. "It feels to me they've got their energy back, they're confident, they're competitive."