It is very depressing to see this amazing facility failing. I suppose the only hope for this type of venture, would be for a syndicate of well off people to run it as a private venture.
Like yourself, a number of people have asserted that it's impossible to run a niche collection in the UK -I disagree.
A number of collections that are niche in some way or other do manage to survive in the UK -Hamerton, British Wildlife Centre, Wildwood, Exmoor (I'd argue the lack of big ABC animals makes it niche), Five Sisters (similar rationale to Exmoor), Shaldon (ditto again, and it's tiny) plus innumerable bird of prey centres.
I'm not saying it's easy or that I know what the answers are* (they're probably different dependent on each collections circumstances) but it can be done.
That said, the situation's still a crying shame.
* though I believe some of the issues for RSCC have been mentioned on this and the RSCC thread