Okay, so no one has mentioned this, but I just read another thread, and of course my computer rebooted when my son stepped on the power cord so now I don't know what thread it was.... but anyway...
It was a suggestion that searches by administrators should include soft deleted posts, and I saw a later post that XF 2.0 does now support that feature if you rebuild your search index.
The post I'm looking for was from 2013 so I'm going to rebuild my index and attempt to search for the lost post. I will report back tomorrow if it worked or not.