When trying to delete a file a pop up message appears and the deletion doesn't work. as expected. My question is what is the expected behavior for a site collection deletion?
How does the retention policy effect a deletion of a site collection? I can enter the SharePoint admin center, mark the site collection and delete it. It goes to the recycle bin and after 30 days it will be moved to the second level recycle bin, but how does the retention policy effects the deletion of the whole site?
Retention Policy only works for the content on those SharePoint sites and not on the Site Collection or the Subsites.
A site collection can only be deleted by the administrators and you don't provide every user with the administrative permissions. Request you limit your user privileges.
Simply you can enable the alert and auditing so that you can get an alert if the admin deletes any site collection or subsites and auditing can help you to view users and administrator activities on SharePoint Online.