(this doesn't appear to be a dupe of Viewing badges, I see “post deleted or otherwise unavailable” or Problem with student badge, which appear to have been specific localised bugs)
Viewing the older end of the list of Reversal badge awards on Stack Overflow, we see that a number of the awards have
(post deleted or otherwise unavailable)
where the link to the answer should be. Now, where a post has been subject to a 'normal' deletion (as with the oldest link on the list, What is your most used .NET namespace? (10k only)), the text is there and the link still works.
So 'normal' deletion doesn't account for these missing links. What does?