title: Deleting document types, content now inaccessible
body: <p>I am learning Umbraco (7) and deleted a test document type and template, without realising there was a content page using these (very surprised Umbraco lets you do this!)</p>
  
  <p>I then couldn't access the content page to delete it (404 error). I created a new page, but that also had problems, almost certainly due to the database now having incorrect integrity, ie links now broken.</p>
  
  <p>Two questions : </p>
  
  <ol>
  <li><p>is there any way to prevent deletions where there are still linked content elements?</p></li>
  <li><p>How would I fix this? Do I need to delete the orphaned content in the SQL backend db using SQL Management Studio? Or can something be done in the Umbraco front end eg scripts in macros?</p></li>
  </ol>
  
  <p>Thanks</p>