code: public function onPageRemoved(PageCollectionRemovedEvent $event)
      {
          $pageName = basename($event->getFilePath());
          $page = $this->pagesParser
              ->contributor($event->getUsername())
              ->parse()
              ->page($pageName);
          if (null === $page) {
              return;
          }
  
          foreach ($page["seo"] as $seo) {
              $permalink = $seo["permalink"];
              $this->permalinkManager->remove($permalink);
          }
  
          $this->permalinkManager->save();
      }
docs: Removes the page from PermalinkManager object
  
  @param \RedKiteCms\EventSystem\Event\PageCollection\PageCollectionRemovedEvent $event