There are various reasons a story is no longer valid. The option to "withdraw" a story should be available.

If the story has not been worked on, closing it is not appropriate. If a story is no longer going to be used or is no longer valid (for many possible reasons), deleting is not a descriptive action either. A withdrawn story could be made available with a filter and show up in regular views rather than having to search within deleted items.

Deleting items may be appropriate for duplicate stories, old stories, or stories that were created by mistake. Withdrawn stories would represent scenarios such as changed requirements/objectives
/priorities. There may be partial work completed but because of changes the story is no longer valid.

This should be accompanied with a comment or reason box that tells the circumstances on why it was withdrawn.