This free "Classic Editor Addon" plugin makes sure that Gutenberg cannot be activated accidentally.
GDPR-compliant: does not collect any user data
The free Classic Editor Addon plugin is targeted at everyone who is not yet ready for Gutenberg and/or who does not want to bother clients with Gutenberg. Install it now on sites and by the time WP 5.0 is released, the UX remains the same as you are used to!
The reason we released the "Classic Editor Addon" plugin is because in the beginning the "Classic Editor" plugin did not what it said on the label.
Since version 0.0.4 of the "Classic Editor" plugin, it finally set the default setting to actually using the Classic Editor. It still contains a Settings page though and if the purpose of people is to get the Classic Editor instead of using Gutenberg, then we don't see the need for such a Settings page.
Also, if we look at developers protecting the sites of their clients with the Classic Editor, they certainly don't want their clients to accidentally turn off the Classic Editor as Gutenberg adds a lot of undesirable comments, tags and what not to the content.
Therefore we highly recommend installing this "Classic Editor Addon" plugin, which will auto-install the "Classic Editor" plugin. It removes the Settings link from the main Plugins page and removes the plugin's Settings from the Settings > Writing screen.