When you delete an index collection from your system, both the index collection and the actual search index that the index collection represents are deleted.
You cannot delete HDDS index collections, you can only unregister them.
You cannot delete an index collection that's part of a workflow that has a running task.
To remove the index collection without deleting the actual search index, you need to unregister it. See Unregistering an index collection.
To delete an index collection:
Click the Index Collections window.
Click the delete icon for the index collection you want to remove.
Related CLI commands - deleteIndex
Related REST API methods - DELETE indexes