The UK surrendering the Chagos Islands to Mauritius has introduced the possibility that the .io ccTLD will be deleted.

https://domainincite.com/30406-five-times-icann-deleted-a-cctld-and-what-it-means-for-io

ICANN's policy appears to make this inevitable if - as also seems likely - Mauritius changes or removes Chagos's ISO3166 code. If it's changed, the registry have at most ten years to retire the domain

https://www.iana.org/help/cctld-retirement

However, no ccTLD that's been widely used has ever been deleted. Previous deletions were of TLDs sparsely used if used at all. .su, for the Soviet Union, is still used 33 years after that ceased to exist.