Wow, I really hope she’s coming back.
I’ve seen the post you’re talking about, which has caused a lot of fangirling today. The speculations are far fetched, but I feel like they may be true. There have been a lot of hints toward it.
For example in the new episode we see where Clara works, a place called The Rose & Crown. The shot of the sign is long, way longer than necessary. That’s called foreshadowing. The writers of this show are clever, and they definitely know how to foreshadow. It fits well with the way we know the show is written.
Then we have that bit of the trailer you’re talking about. That scene was probably one of those classic *head peeks out, then a head beneath it, then a head beneath it*. But in the trailer, they cut it so we couldn’t clearly see who’s the person with Clara and the Doctor.
It may be just be wishful thinking, but I think she may be coming back.