Comment by dmurray

ccTLDs other than .su have been retired when the country they represented ceased to exist or got renamed. .zr, .tp, .cs (twice?) according to [0]

I agree with you though, there doesn't seem to be a strong rule for this kind of thing and all interested parties would likely prefer for .io to continue to exist, so it will continue to exist, probably under Mauritius's ownership.

[0] https://snapshot.internetx.com/en/these-tlds-do-not-exist-an...