Some of my villagers died in my Minecraft world :(

I went caving underneath my house and turned the difficulty to easy, and I guess I didn't light up the village well enough because when I went back up some of the villagers were gone ;_;

It took me a while to realise, I only noticed when I saw the golem was injured and then I went looking for my farmer and realised most of them were gone.

So now I'm trying to make sure everything is lit up, but I'm also making a wall around the village so they can't accidentally wander of the edge of the mountain or into a hole (which has happened before).