The delete/close account module use 4 email templates and below are the names of the 4 email templates
Permanently Delete Account Email in general emails
Permanently Close Account Email in general emails
Permanently Delete Client Account Email in admin emails
Permanently Close Client Account Email in admin emails
To edit an of the email templates, go to Setup > Email Templates and click the edit icon next to the template.
You can also toggle plain text vs. HTML email sending on a per email basis from the editor page.