Several posts for which the Great Answer badge was awarded were erased (for lack of a better term).

(post deleted or otherwise unavailable)

I didn't think it was possible to completely remove posts from the site. In fact, most other posts in that list are deleted and still visible to 10k+ users.

This question is about revision deletion, but doesn't mention whether whole posts can be erased.

This topic is the only mention of that message on MSO, and it was just a bug there.

What's going on here? Is it a bug? Were those posts deleted deliberately? Is it possible (e.g. for the developers) to completely erase posts, and when is this done?