The probem of deleting widgets is more general, it is caused by the developer and the editor using the same backend interface. Similar problems like deleting widgets are 
- inserting images in the wrong size
- adding fonts that were not intended by the designer
- creating more menu items than allowed
.. and many more

The solution is simple, give editors their own interface. And probably the best way to do this is: let this interface look like the website itself. This approach is what I call "frontend CMS"

The [frontend editor][1] plugin is a free plugin that can be used for this. I myself wrote a plugin that takes this philosophy a bit further, [frontendcms.com][2]. It is not free however.

  [1]: http://wordpress.org/extend/plugins/front-end-editor/
  [2]: http://frontendcms.com