Let us see how an organization can be deleted in AzureDevOps.Please follow the below steps to delete an organization

Step 1: Go to Organization Settings and Click on Overview

Step 2: Scroll to Delete Organization and Click on “Delete” button as shown

Step 3: A Popup will be displayed where you will be asked to enter the Organization name again

Step 4: Once you click on the Delete button the Organization will be deleted and you will be no longer able to see the organization under list of organizations once you login

And deleted Organizations can be also restored you can see more about it over here – http://azuredevopsguide.com/restoring-an-organization-in-azuredevops/