1. From the information available it looks like the alert was purged after it Ended, despite it exceeding the 2 week purge window.
2. The URL would lead to the Alert, if it was still available. Notice in the URL is the unique id of the alert, this does not change and always leads to the same alert details page. There is not a different one for different alert statuses.
3. This could be considered for a future release.
Finally, you can configure the email settings so that it doesn't send out email 'Ended' status emails. This can be configured globally, for groups, individually etc.
Technical Support Engineer