andyexeter

Post Lockdown protects your site-critical pages and posts by disabling all non-admin users’ ability to trash or delete them. 
It can also lock pages and posts, which will disable editing of the post as well as disabling trashing/deleting.
The plugin adds a new options page under the Settings menu in your WordPress admin panel which allows you to quickly search and 
select for all pages and posts of any post type. When you find the item you want to select, simply click it to move it to the right 
box and click Save Changes.
See the screenshots for an example of what an Editor would see when they view a list of posts with some locked and protected.

Post Lockdown

Works very well, my only criticism is that private posts/pages should be lockable, ie private posts should appear in the search form.

In order to lock them currently you need to publish them, then lock/portect, and then make it private again

Update!! the developer added the minor feuature request/bug. This plugin is now perfect!

Now perfect

I think the plugin is really useful, otherwise I wouldn't have made it ;)

Great Plugin

Allows admins to protect selected posts and pages so they cannot be trashed or deleted by non-admin users.

Paul Ryan

Limit Revision Publishing restricts edits made by users without the publish_posts capability. Their edits will be saved as an unpublished revision, and the original post will remain published. The All Posts view in the WordPress Dashboard will contain a column indicating posts with unpublished revisions. Notification emails can be sent to a subset of users whenever a new revision has been submitted so users with elevated privileges can publish them. Finally, specific roles can be marked as limited, so any users with that role will be restricted from publishing revisions on all post types. 
Note: this plugin only works with the Classic Editor (TinyMCE). Users of the Block Editor (Gutenberg) will be able to publish any post types granted by the capabilities in their assigned role.

Limit Revision Publishing

Limit Revision Publishing restricts edits made by users without the publish_{post_type} capability.

Post Lockdown vs Limit Revision Publishing