Roundabout Theatre's Broadway revival of Kander & Ebb's Cabaret, co-directed by Sam Mendes and choreographer Rob Marshall, opened less than a week ago, and already the talk has turned to replacement casting once the leads' contracts expire.

Cabaret opened Mar. 19 and has been extended to November.

That's because Natasha Richardson's contract runs only to mid-May, 1998, at which point (says production spokesperson Erin Dunn), she has the option to extend her engagement as Sally Bowles.

One thing that might keep Richardson in NY longer, though, is that her husband, Liam Neeson, will be starring in The Judas Kiss on Broadway throughout the summer. Richardson and Neeson met when they starred together in the Roundabout's Anna Christie.

Scottish co-star Alan Cumming, as the leering emcee, is signed with the show through September. For tickets ($50-$75) and information on Cabaret at the Kit Kat Klub on West 43rd St., call (212) 719-1300. Tickets are also onsale at the Roundabout box office but not at the Kit Kat Klub box office. Evening performances begin a half hour earlier than usual, at 7:30 PM.