This actually makes me happy in that Steph doesn't just pick up the Batgirl costume after Cass quits and try to replace her; Cass picks her, literally hands her the costume and tells her to do it. I think once the decision to make Steph Batgirl was made, this sequence is the best possible transition as far as respecting Steph and Cass's relationship.
I have mild hope that the "No more" is with regard to fighting as a bat, and she's going to find a non-bat role (either a new one or Nightwing as suggested by someone here previously) for further awesome team-ups with Steph.