After abruptly disappearing to rehab last month- leaving Friends and his current film project Servicing Sara (with Elizabeth Hurley) in the lurch- Matthew Perry is back at work. The actor returned March 20 to the sitcom's Warner Bros. lot, where cast and crew were putting the finishing touches on the season finale, an episode in which Perry's character Chandler may- or may not- marry Courteyney Cox Arquette's Monica. Details about the television wedding remain a well-guarded secret, much like information about Perry's treatment. This much is known: Friends is slated to wrap March 30, with the "wedding" show set to air May 17.

Meanwhile Hollywood's other notoriously wayward son, Robert Downey Jr., has been dutifully punching his time card on the Ally McBeal set. (Downey has three more episodes to film.) Despite the fact that he faces a preliminary hearing on drug-possession charges April 30, "we expect Robert will be in every episode for the rest of the season," says Ally rep Chris Alexander.

But considering that production delays- say, from an AWOL star- can be costly, isn't hiring vice-prone talent risky business? Not necessarily, says Maureen Duffy of Film Finances, a bond-completion company covering budget overruns. Despite his history, Downey has "always been bondable," she says, because he has never let reveling interfere with work.

Perry is more of a gamble. He may face higher insurance premiums and restricted coverage and even be assigned a "shadow"- someone to tail him and ensure he stays clean. Still, "every situation is different," says Duffy. "I don't know that he'd be a red flag."

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