Or am I overthinking it and it's going to be Cena taking out the entire team himself after his teammates all get beaten up backstage?
How would you utilize Orton at Survivor Series (I'm going to go out on a limb and say that he can probably get the day off from filming "12 More Rounds" or "Oculus II: Oculii" or whatever direct-to-Chinese landfill he's working on now)? Let's say the match comes down to Cena vs. Rollins. Let's say Rusev gets counted out or something (gotta keep him strong before he does the job at Wrestlemania). He cheap-shots Cena before he leaves and that seemingly gives Rollins an easy pin. Orton comes down and everyone thinks he's going to attack Rollins. Instead, he beats on Cena causing Rollins to be DQ'ed and the Authority loses their power. It preserves Rollins (how long has it been since he's been pinned, anyway - was Reigns the last one to do it?) and it doesn't make Orton a sugary babyface since he didn't help Cena. Plus Cena stands tall at the end of the show, and that's how all WWE special events have to end, right?
Yeah, I think you're overthinking it. Orton isn't showing up because they've been super-careful to remove him from all advertising. I know there's a feeling that the Authority will win again to maintain the status quo, but I'm still pretty sure CENAWINSLOL as you described to "keep him strong for Brock" and so that the announcers can freak out about who's running the show while they tease out a new GM to pop the ratings from 2.5 to 2.6.