Hey Paul, sorry to hear about your save file troubles.
Save games are actually stored on your machine, not on any server of mine. In a case like this, what probably happened is the power went out just as the save file was being updated, causing it to be lost.
(If you've played console games, they often tell you not to cut off the power while they're saving, or while a certain icon is on the screen, this is the same kinda deal.)
In such an event, there would not be relic wraith since the server was never notified of the death. (There is no key to view relic wraiths, and causes of death aren't noted either, since that isn't necessary for building them.)
System Restore...might?... work? Nobody's ever tried it that I know of, but since the files were on your computer, it's possible they'd get saved.
I'd offer to try restoring the file from your save data folder if you sent it to me, but this has a pretty much 0% success rate in my experience: usually the files left behind after a power loss incident are just blank/null data. Still, if you send it, I'll take a look.
ferretdev.org@gmail.com is the address. On Windows, they'll be stored in a directory called Users\[accountName]\AppData\Local\FerretDev_Org\Demon\Save_10_27_19, where [accountName] is your account name on the machine. Zip up and send that entire folder to the e-mail address if you like, and let me know which save slot the game was on.
Sorry I can't be more optimistic about things, losing a game is pretty terrible.