Minecraft villagers gone?

In Minecraft, all of the villagers in every village are gone. Also have peaceful so it's not a zombie attack. Can someone tell me why they are gone or how I could possibly save my world, because there's a lot of work there.

After a while, all mobs will despawn.

in retrospect you can only cheat them back (in creative mode)

To prevent this in the future, you can name all villagers in the future

(name tags can be found in dungeons or when fishing with a fishing rod with luck of the sea)

Yes the problem is the villagers don't exist from the start, thanks anyway.