20w07a deleted all of my villagers.

I've been playing on a map that's endless Snow Beach.  Over the past few months, I've managed to rescue and create up to 30 villagers, many of them expert-level traders.  But tonight, after the 20w07a snapshot uploaded to my computer, when I turned the game on, I found all of my villagers gone.  

This was upsetting, because those villagers were pretty much the most precious thing about that map.  I built a bustling city in a world of barren sand and snow.  

I backed the game up when I was prompted to.  But when I load the backed up game, the villagers are still gone.

Keeping the villagers alive, thriving, and protected gave that game purpose.  But now, I don't seem interested anymore.  Is there a way to recover these villagers?