I still think it's possible Ashildir could be the new Companion, with the Doctor seeing the need to keep an eye on her now.
I disagree. For one thing, I think Ashildir will be lucky to survive the season. For another, the Doctor has been known to hold a grudge and he has no drive to give a shit about Ashildir at this point. I think he'd be more likely to Family of Blood her than give her a spot in the TARDIS.