If the Casson building cannot ever be opened again and they cannot ever afford to rebuild the Mappin terraces, why not move all the childrens zoo animals to the Lower Mappin level and outside paddock of Casson (neither of which can be listed due to recent changes, then bulldoze the whole childrens zoo area, move the Squirrel monkey to the Snowdon aviary,use the former anteater enclosure for animals again, build on all this plus the bird of prey event lawn plus neighbouring grass areas for some proper zoo mammal attractions?! Turn the woodland walk to the picnic area to replace lost lawnsYou may even have a top 5 UK zoos again!
This is subject to not having listed buildings status removed which would probably be preferable sadly!