Anthony Borrow brought it up :
"
Is there for an admin deleting a block which may be a dependency for something else? I'm wondering if it might be helpful to have a database table of dependencies to check against.

Here is what happened that made me think of this: I was receiving a PHP notice for a block (in this case formal languages) which the correctwriting question type lists as a dependency. After deleting the formal languages block I received a PHP error that prevented me from accessing the blocks page.

I think we may want to do better at protecting admins from potentially breaking their site - we do not allow addons to be installed that do not meet the dependencies, I think we should check for dependencies when attempting to delete a plugin
"

We just need to re-invoke the dependencies check when deleting.