Ultimately this just seems like a generic answer most zoos give when it comes down to the future of a species at a zoo.When was it confirmed?
I visited back in May and did the Elephant Insider Tour and when I asked the question of the future of their elephants the keeper responded with plans are ever changing. Since there is such a large age gap with Karnaudi and the rest of the girls only time will tell if they bring in more elephants or move Karnaudi on when the time comes.
In saying that though, this is somewhat still accurate as plans with zoos do always change. Whilst right now the plan may be to phase them out, there may be a change in management down the line that may wish wish to invest in a completely new herd. Especially considering elephants are such long lived animals it's difficult to predict where the zoo will be at in say 20 years time when the current herd are in their final years.