Michelle Gomez was at the London Film and Comic Con this past weekend, and she was of course asked whether Missy’s coming back…
But she says she doesn’t know! The actress explained:

“I just don’t know. I mean, I don’t even know if she’s coming back this season to be honest. As a freelancer – which is what I am – I try to bag the next job, do it as well as I can, and then move on to the next one.”

Hmm. This sounds quite a bit like a white lie to me: if she is coming back, she’d surely have already been asked, right? After all, they’re filming the third episode right now (penned by Face the Raven‘s Sarah Dollard), so the scripts for the rest of Series 10 should either be in the bag or pretty darn close to finishing. Mind you, Peter Capaldi says they’re shooting for 10 months; maybe the final stories are still being batted around?
Nonetheless, Gomez should’ve been asked to at least keep some of her calendar free for potential filming. You can’t blame her for possibly fibbing: the BBC production team like to keep things hush-hush, and there’d likely be some sort of clause in her contract about keeping schtum.
Michelle debuted as Missy in 2014’s Deep Breath, and was last seen in 2015’s The Witch’s Familiar – faced with Daleks on all sides, Missy had a clever idea… But we don’t know what it was yet.
So would Michelle be up for appearing in Doctor Who spin-off, Class? She only teases:

“I am an actor for hire, so if I’m free and it seems like the right thing to do at the time I’d grab it with both hands.”

Yep, keeping coy.
Would you like to see Missy back? How about a Twelfth Doctor vs. Missy showdown at Christmas? Or would you rather the show ignore that part of the mythos for now?