I don't expect they will either, with the focus nowadays on zoos maintaining family-related groups. Though if a group is dwindling as Chester's is rather, it should still be possible to add new females from time to time if the need arises. Birma was a failure, though it was never exactly explained why really. I know she had been alone for some while in her previous zoo in France though and apparently it was an integration problem. Maya and Jangoli were both cows that came from other zoos as adults too, and were added to Chester's group successfully in the past, though that was at an earlier stage of the group's formation. But like you I imagine it will just stay as it is, providing there are no new losses.