I have been reading a journal article that extensively references another article by the same author. The cited article is referenced to a pre-print service but it has now been removed. I had no luck finding it through other searches so I requested it directly from the author. I received no reply for months despite following up a few times. In the end, I managed to call the author but was told, very abruptly, that the reference was not available.
The question I have is what are the ethics of essentially deleting a reference from literature that remains used to justify a subsequent article? I know some articles don't progress but deleting them seems extreme.