Why not extend the current enclosure all the way back to the rhino paddock and across to the old red brick houses currently used for Capybara/Tapir/Anoa and 'Winter Ostrich'?' Then, as someone pointed out earlier on, it could house a 'retirement herd'?
If Elephants are not in the 'masterplan' then that whole area from the Badger Hide across to the back of Monkey Heights and up to the camel and Barbary Sheep, and above the cheetahs area, could become one huge African exhibit with overhead walkways?
It always amazes me (and I'm sorry to pick on your post for this, TriGB!) how the first thing so many people think of whenever changes are afoot is 'how many areas can we lump together into one big exhibit?'! All that happens is that that one big exhibit takes up half the zoo and reduces the number of animals and species on show. Better to lose one big species than 15 or so smaller ones, in my book.
For the short term, I suspect Duchess will live in solitary retirement; unless she seems to be reacting adversely to being on her own I suspect bringing in other animals may be prohibitively expensive (although, of course, this depends on what the zoo's future elephant intentions are).
If the zoo do not intend keeping elephants once Duchess dies, then I would expect the giraffes to be given the whole house and paddock, possibly with the addition of one or two other species (preferably browsers rather than grazers, at least while the paddock recovers!).