Was this a freak occurance?
Can't say for sure as I've only played two games, but I suspect not. The last game I played with the tavern was a 5P. We had three drinkers and I pulled the card that increases the bonus for people in the chronicle very early in the game. I was killing people very quickly, to the point where there was no room left in farms or crafting by the end of the second round and then add three drunkards in the unmarked grave on top of that. I could have ended the game near the end of round two, but instead I used a marriage action to relocate the meeple who would have been the last unmarked grave. As it turned out, we extended the game into the middle of round four, but only through a concerted effort of everybody.
There does seem to be a change in balance with the graves if the tavern is in play. If all players send a worker there, that only leaves one unmarked grave available for other purposes. I'm becoming less enchanted with the expansion buildings the more I think about how they affect the game.