And it doesn't matter what the registrars choose to do when the entire ".io" TLD gets kicked out of the root name servers - who in turn are following the official zone file as published by ICANN.

Accepting registrations for a domain is pretty useless when those domains aren't going to resolve to anything.

But do the root name servers _have_ to respect the ICANN zone file?

at least one of the root name servers is hosted by ICANN, so there's essentially zero chance that all of the roots will choose to disrgard the ICANN zone file.

If an ICANN decision would be seen as detrimental to the smooth operation of the global DNS network yes there is, their server would simply be quarantined yes it would be a problem since root servers are “hardcoded” in many places but for the most part all the major DNS services can continue to operate without them for a while at least.

A bunch of startups losing out on domains they bought despite best practices is not an event I would call “detrimental to the smooth operation of the global DNS network”.

This was a known and willfully ignored business risk for these places.