I do not think we added codes to handle delete condition.
To be honest, we missed it! But in a way its good NOT to handle this condition as:
1. Any change in map.conf requires nginx service to be reloaded from command-line on server.
2. Deleting a site but leaving map.conf line for it won't break nginx conf.
3. On next site creation, map.conf will be regenerated without lines for deleted sites (if entries for them are deleted from wordpress site/blog tables)
Still, if you wish to add a handler for delete condition, please feel free to do so.
You may send a pull request of your changes at https://github.com/rtCamp/nginx-helper
Please make sure you add a setting like "Regenerate map.conf when a blog is deleted" so that users have option to enable/disable this.
If I missed anything here, please let me know.