I was able to repeat the event by loading the previous auto save, yes.
But unless I botched which save I chose, the third time I did it, and left my Sovereign in my capital for two more turns, the loss never happened. Still, even when I continued after the loss, the capital was still there.
Despite all of this, that game over cut-scene with the map and fade to black? Holy crap what a disappointment! I thought it was a bug as well because I had no idea what was going on, and then it just abruptly ended.
EDIT: I just checked a save game I have. If I load it and press "end turn", I hear the giant crash and see the cut scene... still no idea why.
