The more that I have mulled over this, the more I feel upset by it, as seems to be the consensus here. As some will know, I tend to defend ZSL avidly, and am very much an optimist where they are concerned, but I can't remember ever feeling so bewildered and disappointed by something from either zoo. There were some delightful species lost, such as the hummingbirds or bearded pigs at London, but that was due to animals passing away and a European phase out, or the Aquarium closure which was very clearly not a fault of ZSL with the costs of keeping the structure operating.
But why the zoo would not chose to find new hippos is just bizarre. I understand that the EEP recommendation necessitates the move of Hodor and Lola to Longleat, but why no replacement? Running costs of filtering the water? Lack of availability of other animals in Europe? I just don't understand. They are massively popular among visitors and there is
nothing else comparable to them. I mentioned this in a previous post but they, along with the moose and the gaur, were always in my personal 'big three' of large mammals at Whipsnade. Large, striking and unique animals which are kept at very few other UK zoos, and no other zoos that I visit even somewhat regularly. The moose have been gone for a while now, the hippos have just followed suit, and I can't imagine its long before the gaur do as well (although of course there are suggestions that the phase out here may have been reversed, so time will tell). Of course, the quality and charm at Whipsnade will never fade, and it will still remain one of the best zoos in the country, but seeing big mammals that are hard to see elsewhere in field-like settings where they just look so at home and well-suited is, ultimately, what makes the place special, and I think the hippos were among the very best that the zoo had to offer in that regard, as were the moose and as are the gaur.
My inner optimist and ZSL defender looks at my rant above and feels as though I am hugely overreacting to the departure of a single species, but I just feel as though hippos are such an important species, and one of the few that has nothing even remotely similar to it (except of course Pygmy Hippos which the zoo already keeps). Of course there are still elephants and rhinos for that sense of awe and wonder, gemsbok and forest reindeer to offer rarer species, and a lot more, but the truth is they're just
not hippos, and nor will whatever goes in the former hippo enclosure be. I agree with what
@Lafone is saying that it is nice that to see as a Whipsnade local that an ex-Whipsnade hippo is crucial for rebuilding the UK population, but rather selfishly, as I don't have a car and will probably never visit Longleat again, it doesn't effect me, and I find myself frustrated that to see this species, which 15 French collections, 14 Spanish collections and 13 Italian collections hold, I must travel overseas, go to a theme park in Yorkshire or hire a car and go to a safari park to see. And I never thought that I'd see the days where there are more UK holders of Polar Bears than there are of Common Hippos!
Purely as a species, I like the upthread suggestions of Giant Otter and Malayan Tapir, but for me the zoogeographical arrangement is an integral part of Whipsnade these days. I would make an exception for Polar Bears, though!

So for me, the only real options would be: a) continue the African rainforest themes set by the Pygmies next door with something like Okapi or Congo Buffalo, b) something that would make the most of the open, sloping, meadow-like design of the enclosure such as Gelada or, likely incorporating the offshow paddocks behind, Black Rhinoceros, or c) something that would utilise the water body at the bottom, like Sitatunga, which would be lovely but
not a new species for the zoo, and therefore not able to fill the void left in Whipsnaders' hearts by the missing hippos. It would be nice if there was some sort of giant African tapir to tick all the boxes, but there isn't. I feel as though the zoo's options are somewhat limited, but seeing as we have gotten Small Indian Mongoose at London recently, I trust them to bring something somewhat interested in. Perhaps they'll rebuild the entire thing as a great big aquarium for manatees and all will at once be forgiven.
An apology for what turned out to be a very long-winded rant and, for quite possibly one of the first times ever, being negative towards a decision made by ZSL. Again, I understand that there is probably a reason behind this decision, but I felt as though I needed to get all this off my chest!
EDIT: Does anyone know what date Hodor and Lola will be leaving Whipsnade? Just saw one the website a suggestion to visit one more time to pay them farewell, and realised which that may not be a bad idea if at all possible...