Alcohol and drugs within Hollywood is not a new thing. The question is, how does it affect the actor's career and the projects he or she is working on. The Hollywood Reporter has posted an interesting article regarding the possible impact of Charlie Sheen entering rehab on the production of 'Two and a Half Men.'
The summary is this: if Sheen has a "morals clause" in his contract, then his behavior could cost him his job. His character is fairly central to the show and the absence of it would be noticeable to the viewer. The producers could use this as an opportunity to renegotiate his salary.
Also, the producers likely have insurance on him in the event of a circumstance like this (particularly given his past behavior). So there is a safety net.
When Sheen took over for Michael J. Fox on 'Spin City,' the show lasted two additional seasons before cancellation. If applied to 'Two and a Half Men,' that would make for nine seasons. The show is already thriving in syndication. What do you think they'll do about Charlie's troubles?