Today (18th February) was the day originally planned for the Radix team’s archive nodes to be deprecated and moved over to the new Gateway service. However, in the interest of ensuring a means of unregistering a validator node (in the event a node falls out of sync), the Radix team have confirmed that the shutdown of their archive nodes will be delayed.
An update to the Gateway service to enable unregistering of a validator will be made prior to any shutdown of the archive nodes. In the meantime, if a node runner needs to unregister - this post by @Stuart still applies as long as the archive nodes are still available: Unregistering a Validator
This is a sensible decision. I’ve seen the update to allow a node to be (un)registered on the gateway has been merged so should be available in next release.