by Brajesh Singh on WordPress.org
Disable Site Delete plugin completely disables the site/blog deletion by a non network administrator

No Delete Menu for Non Network Administrator screenshot-1.png.
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:-
Need more details, please visit this post on BuddyDev