Ok, first things first, I don't believe that's the end of Clara. Yeah, they made a big deal of her saying goodbye and it was all really emotional, but when it comes down to it it was a pretty nothing death. I don't think they'd write out a major companion that way and, tbh, I'll be really disappointed if it turns out that that was her actual end.
I may be reading too much into things, but I'm convinced that the fact the raven went into her front is significant. Everyone else runs away so the raven flies into their backs and just kills them. But Clara faced the raven (like the title of the episode says) and I just feel like that has to be important.
I don't think she'll just come back to life, because that would be cheap, but I do think something else is going to happen with her.
I'm still clinging to my theory that she becomes something else in the finale, so maybe she joins up with the raven. Maybe she becomes a shade too. Maybe she becomes a hybrid with it because god knows they've not been subtle with all the hybrid references throughout this series.
I'm also wondering what's going on with Ashildr. At the Doctor Who Festival Sarah Dollard said that she had to change out her original antagonist for Ashildr when Steven Moffat decided this would be the episode leading into the last two. But why? There was nothing specific to Ashildr in the role, anyone could have done it, so all I can think is that she's coming back. That there's a link between her and the mysterious "they" who made her trick the Doctor into turning up so they could abduct him. Her story's not done yet either.
I don't think she'll be the next companion though. I don't think she could move from this role into the companion role, and Maisie Williams is probably too busy with Game of Thrones to have time to be a main character in another show as well.