The UK will give sovereignty of Chagos Islands to Mauritius:

Half a century or more after the UK relinquished control over almost all its global empire, it has finally agreed to hand over one of the very last pieces. It has done so reluctantly, perhaps, but also peacefully and legally.

The Chagos Islands are also known as the British Indian Ocean Territory, to which the .io ccTLD is assigned. Given that the UK is relinquishing control of the islands to Mauritius, there will no longer be a British Indian Ocean Territory, raising questions about the popular .io ccTLD.

Simon Willison summarizes the Hacker News discussion on his weblog:

It sounds like there’s a very real possibility that .io could be deleted after a few years notice - it’s happened before, for ccTLDs such as .zr for Zaire (which renamed to Democratic Republic of the Congo in 1997, with .zr withdrawn in 2001) and .cs for Czechoslovakia, withdrawn in 1995.

The Wikipedia article for the ccTLD is also informative.