That scenarioo has happened a lot. I had a village that was fine when I went to bed, but by morning all of the men had mysteriously disappeared.
You have to wait and hope for an event to bring more villagers, such as a crate o' babies or sometimes if you get lucky a farmer comes out of the trees.
I would suggest keeping the ones you have working and trying to get all of the med techs if you don't have them already, then at least the villagers will live longer giving you more chances at the right event.
Also, keep the game running on 1/2 speed.
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Why is it that if someone tells you that there are 1 billion stars in the universe you will believe them,
but if they tell you a wall has wet paint you will have to touch it to be sure?