Just what I was thinking on your first point
As for your second point, I believe that any animal can be kept alive in captivity, it's just we don't have the experience or knowledge to care for some (or at least didn't in some cases and do now).
It was considered difficult/impossible to keep Sumatran rhino alive I believe, but now that Cincinnati has the experience and the knowledge they seem to have done a decent job, even having 3 calves before losing their breeding female Emi.
It was also considered impossible to keep three-toed sloths due to a difficult diet, however now that this diet has been cracked I believe there is somewhere in the states exhibiting them?
I think it was Monteray Bay Aquarium (not sure) even manages to keep Great white sharks alive longer than was ever expected (though not indefinately, any sharks have been released after time - is it a rescue?)
I would imagine that some species that died out in captivity due to difficult husbandary could be successful if anybody took the first step to trying again (though I stress not all of them).