Starling’s removal from BoP seems to have been, like most narrative irritations in the New 52, ordered by editorial. Ev’s return, however, is not completely out the question, it seems.
From series writer Christy Marx’s interview with CBR:
CBR: You’ve also mentioned that you’re introducing a new character coming up in the series, and your run began as Starling left. For you, how important is it to have a rotating cast around Dinah? Do you see the Birds Of Prey as similar to Suicide Squad in that during any mission they may lose or gain members?
Marx: Letting Starling go was something that had been established for the series well before I began work on it. My inclination is to keep the team more stable rather than rotating people in and out. That’s not to say it won’t happen, but not in the near future. I want to explore this set of people more deeply before making a change. Also, I don’t want to make a change just for the sake of making a change. It should feel organic to the story and make sense.
CBR: Similarly, do you have any interest in bringing back old team members, like Poison Ivy or Starling?
Marx: I don’t have an interest in bringing Ivy back. She is, pardon the pun, a toxic character. I definitely want to have a rematch with Starling and have some plans for that.