American Idol is once again becoming more compelling for its backstage drama than its onscreen singing competition. Sex-obsessed sexagenarian Steven Tyler is out. Poised pro Jennifer Lopez says she’s gone too. The fate of snoozily affable Randy Jackson, who’s managed to survive years of high-profile shake-ups on the Fox hit, is uncertain. One thing is clear: American Idol will be reinvented again before the 12th season launches in January. Though Tyler’s departure was announced last week, the decision to overhaul the show was effectively made months ago, when the 11th season suffered the biggest ratings drop in the series’ history. Idol was down 23 percent — to 18 million viewers — from the previous year. That’s still a large enough audience to make Idol TV’s biggest non-sports program, but it’s an alarming decline for a costly show that’s critical to Fox’s schedule. Though deal-making is still in flux, the current front-runner to replace J. Lo is Mariah Carey, with Janet Jackson, Katy Perry, will.i.am, Kanye West, and Fergie also on Fox’s wish list. Sources say Carey is deep into her talks with Fox and would probably score a paycheck on par with Lopez’s. (Negotiations started around $12 million a season, the same as Lopez’s first year, though they will likely conclude closer to Lopez’s second-year rate of $15 million.) While there have been reports that the network might dump Randy Jackson, insiders expect him to stay if Carey comes on board (Jackson manages the pop star). As for Lopez, the singer still claims she’s leaving, but as of press time Fox hadn’t given up. Lopez gave a vague interview on July 16 that left some wiggle room (”I don’t know if it’s even done yet,” she told GMA of her departure), and Fox has tried for weeks to persuade Lopez to stay for a third round. Still, sources say it’s unlikely that more than one megamillion-dollar diva will wind up at the table. So if the network can land Carey for less than Lopez’s current price, expect a lot of contestants to sing ”Dreamlover” next season. For the third seat, Fox is considering a lower-budget option: former Idol contestant Adam Lambert, who could bring a sharper edge to a panel that’s been knocked for being too soft in recent years. And Fox Entertainment chairman Peter Rice plans to continue cutting costs across the board (offscreen cuts were made last season, too). Even if the Idol reorganization doesn’t boost ratings, the show is strong enough to survive another 23 percent drop next season. Such a decline would give it roughly the same size audience as TV’s second-biggest singing hit: NBC’s The Voice.