Send e-mail when webform submission changes
If you look here : http://drupalcontrib.org/api/drupal/contributions!webform!webform.api.php/group/webform_hooks/7 , you'll see that Webform provides some hooks on which you can act. 

There's a hook called 'hook_webform_submission_update', which triggers on the update of a submission. Using that one, you can check if the boss approved/denied it, and send out an email.

The plain 'send email on submission' can be configured through Webform itself, so you won't need to use a Webform hook for that. Although you could if you want to.