How do you replace the show’s star?

When Charlie Sheen was fired from Two and a Half Men (for what his studio’s lawyers described as “shocking behaviour”), the world began arguing over whether the show would replace him or simply never film another episode. But in a more quiet way, other shows were already preparing to replace stars who aren’t Vatican assassins. The Office is doing a story arc that will lead to the exit of Steve Carell, who announced a year ago that he would not be renewing his contract. And the nudity-filled cable drama Spartacus: Blood and Sand recently hired a new actor to play the title role after the original star, Andy Whitfield, announced he had cancer.

Fans of a show often would prefer it to be shut down rather than see it change too much. Salon.com critic Matt Zoller Seitz implored The Office not to go on without Carell: “He is The Office, for better or worse, and anything after his departure will necessarily feel like a postscript.” But that can’t happen unless a network has something better to put in the show’s place, and The Office, Two and a Half Men and Spartacus are all among the biggest hits on their respective networks.

That means when the star is unavailable the writers will have to find a way to carry on. Most shows, unlike Spartacus, prefer not to recast the main character. The X-Files responded to David Duchovny’s departure by bringing in an actor from Terminator 2 to play a very different lead. When Valerie Harper was removed from her self-titled show Valerie, the producers killed off her character and changed the name to Valerie’s Family. Chip Keyes, one of the showrunners on Valerie, told Maclean’s that a situation like that is hardest on the writers, who have to “break stories and prep scripts that include an as yet unknown main character and actor,” and that his team had to shoot an entire episode without knowing who would star in it: “We’d shoot those scenes later and drop them in.”

Though it’s hard on the writers, a show can sometimes be reinvigorated when the star leaves; the writers have to work harder on restructuring the show, and sometimes find new ways to approach it. Keyes says that without Harper, he and his colleagues were able to give more attention to the rest of the cast, particularly a young Jason Bateman: “We were pretty sure the rest of the ensemble, led by Jason, could still carry the show if it came to that.” Paul Lieberstein, current showrunner of The Office, told Josef Adalian of New York magazine that the writers are having fun trying to shake things up: “We’re having the kinds of conversations we had in seasons one and two about, ‘What is the show?’ ” A long-running show can feel tired and locked into a formula; in the mad scramble after the star leaves, the writers have a chance to, as Lieberstein put it, “really influence the show in a way we couldn’t last year.”

But there are also cautionary tales. As a mystery show with a large cast, CSI seemed well-positioned to go on without William Petersen, yet ratings have tumbled since Laurence Fishburne replaced him. This can be a problem not only for future episodes, but for a show’s value in reruns. The Office and Two and a Half Men are two of the most-watched syndicated sitcoms, but they might not be quite so popular if there are a few dozen episodes floating around without the star.

That fear could help explain why Two and a Half Men shut down for the rest of the season rather than film episodes without Sheen. But it doesn’t mean there are no contingency plans for going on without him next season. TMZ.com reported that Rob Lowe was in contention for a similar role on the show, while Keyes thinks there’s no reason the writers couldn’t simply take a cue from Jason Bateman and build up the role of Sheen’s underrated, Emmy-winning co-star: “When something on that show makes me laugh out loud, it’s usually Jon Cryer.”

Whatever the producers do, they can always take solace in the example of Spin City: when star Michael J. Fox had to step down due to his Parkinson’s disease, the network replaced him with a washed-up movie actor—and the show did so well it ran for two extra seasons. That actor’s name was Charlie Sheen.