Hi,
you can disable
Versions tab in Properties of documents using
UI personalization module. Without access to this part, CMS Editors role will not be able delete versions of document.
Unfortunately, in the UI is not an option to cancel or revoke the request. There is a Preview mode, where the editor can check page content and decide if he finished his work or not.
In case you need this functionality in your project, you can use API and add this possibility into the UI. You can find API examples
here.
Best regards,
Ivana Tomanickova