Is this some sort of an easter egg? I saved my game, the date on the save says it's 1400 / 6 / 6 6 - then I proceeded into doing something else. A grim reaper popped up saying "death strikes swiftly", and then a ghost came out of a skeleton(???) and the game shutted down. Anyone else run into this? :D Luckily my save didn't go awry. I have not formerly played this much and bought it just out of interest into the theme (and with some hours put into it I'm liking it too) so I don't know if this occurs somewhere else.

That's what happens when your entire party dies.

Okay. My party didn't die as far as I know (and I haven't played enough to have any of my games end in whole party dying), I was still in my starting town and was going to the market after saving IIRC and then the cutscene just popped up. I thought it might have had something to do with the in-game date of the save :D

If you go to load a save game but cancel out of the load screen, you will go back to find your party has vanished (your characters unload when you go to the load save screen, which is why the "Loading is irreversible" popup appears), and you'll get the Death Strikes Swiftly game over screen. That may've been how you got it.