BuddyDev

Brajesh Singh

Disable Site Delete plugin only allows network administrators to delete a blog/site on a WordPress Multisite network. It does not allow blog owners to delete their blogs.
It works by doing that in 3 steps:-
<ul>
<li>Removes the delete Site link from tools menu for non network admins</li>
<li>Breaks out of wpmu_delete_blog function to avoid deletion of blog</li>
<li>hacks around option to avoid sending the delete confirmation mail to blog owner</li>
</ul>
Need more details, please visit this post on <a href="http://buddydev.com/wordpress-multisite/introducing-disable-site-delete-plugin-for-wordpress-multisite-based-networks/" title="Introducing Disable Site Delete plugin" rel="nofollow ugc">BuddyDev</a>

Disable Site Delete

a good simple plugin that does what ist says and does not try to do too much

Works as stated

Disable Site Delete plugin completely disables the site/blog deletion by a non network administrator

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.

Disable Site Delete vs Post Lockdown