I disagree with Tuta in this case. The Soviet Union and Yugoslavia are not precedent for what will happen.
In fact, it is precisely because of those two situations that IANA is far more strict about this policy now. If .io is removed from the ISO 3166-1 alpha-2 list there is zero doubt in my mind that the TLD will go away, so I would not be as confident as Tuta is here.
That being said, I think it is very possible that the ISO will decide to make an exceptional reservation for the IO code keeping it in place forever, although I’m not quite sure how they’d justify doing that. Maybe simply being asked to by IANA is enough.
IANA’s policies are clear though, it is up to the ISO to determine what two-letter TLDs are allowed to exist, not IANA or ICANN. I kind of expect it to become a transitional reservation and be deleted in 5 years, personally.
DO