Lots of people lost their domains when .tk (and the many other free domains) died and got reborn. There's a list of ccTLDs that died. .yu expired in 2010. .zr

Lots of people lost their domains when .tk (and the many other free domains) died and got reborn. There's a list of ccTLDs that died. .yu expired in 2010. .zr moved mostly to .cd in 2001. Perhaps .io will not disappear immediately, but it can definitely fall under new management, possibly with double or triple the already high fees for good measure, or registrations will be restricted to the people of Mauritius. A TLD will not keep existing just because people use it, especially a TLD belonging to a specific government such as .io or .ai.