If you delete a folder, all the items inside it will not be deleted and can be accessed from the All pages/post/files etc. To delete items, you need to select the item and delete it using the native WordPress delete option. E.g:
To learn more about how to use the plug-in click here, and don’t forget to check our entire Folders knowledgebase to make the most out of it. Here you can read if Folders changes the URL of your media/ posts/ pages and by clicking here you’ll learn how to delete a folder.