Once in a while WordPress Multisite admins may have to face the fact that blogs are not forever :)) Some authors may choose to delete their sites from the network.
Once they use the option to delete from the Tools menu they will receive a message like this one:
You recently clicked the ‘Delete Site’ link on your site and filled in a form on that page.
If you want to disable this option and keep your bloggers captive :)) here you go: Disable Site Delete – a plugin that does just what the title says.
From now on your bloggers will have to ask you to delete their blogs as super-admins will be the only ones being able to do it.