Yes, it will really change the impact of the exhibit when Kipper goes. The Sea Lions are so much bigger and more interesting to watch underwater than the fur seals, so I think the popularity of the exhibit will decline. They should get some Hooker's in. Rescue ones of course.
I would very much favour for them to have a local pinniped species. Would constitute another great conservation story, even with rescuees. Hooker's would be a nice addition!