Clara's not that bad. Not my favorite, but she's still kinda fun and amusing. Besides, I think it's already been explained at the end of season 7, before the specials: she's seen 11's timeline. Everything that had happened to that point. New doctor to me means, new timeline, so odds are that once she's dead under 12's timeline, she won't be returning unless Moffatt comes up with some sort of caveat to that.