Delete wordpress user when related Civicrm contact is deleted
In general there is a risk of having a CMS user deleted when the CRM contact is deleted, since the CMS user can (in theory) be the author of pages, comments etc

Therefore Civicrm does not offer this directly and I think you would need to find/make a customisation/extension or see if there is a tool in WP that you could use that would make it easy to find all WP users that are not connected to a civi contact and then delete them (there are solutions for this with Drupal using Views and VBO, and potentially also Drupal Rules in case any of that provides hints for WP)