When a notebook is shared, a specific shared version will remain accessible through its version identifier, even if later on a newer version is shared or published.
When a notebook gets unshared or unpublished it becomes completely inaccessible to other parties. However, resharing the notebook will not restore access to previously shared or published versions.
Given their proximity to “View history”, the options “Disable link sharing” and “Unpublish” are prone to be triggered accidentally. Due to their destructive nature (as described above), executing them should require additional confirmation (just like “Enable link sharing” does).
Note: Ideally I’d prefer these options to be non-destructive, i.e., access to shared versions can be restored, but I’m assuming that a modal is a lot easier to implement.