Steam user Amallah discovered that a dev build was left in the game's files, which seems to be at least basically functional. From my own testing you can indeed load into and play on maps, though I haven't been able to test if multiplayer works.

To access the dev build, go to the game's installation folder and travel to steamapps\common\Obsideo\Obsideo\Binaries\Win64 and launch HorrorGame.exe

Shrimple as that. Shoutout Kyle for killing the game randomly and going back into absence again.