Minecraft Villagers vanish

What happens is that villagers despawn without a name tag, so name your mob so that it doesn't just dissapear.

There are a few possibilities to what may have happened to your villagers:

1. They escaped the structure they were contained in. Villagers will automatically try to find the nearest route to their job site, which is a job block (such as a fletching table or a lectern). The ravager may have broken a few blocks of the wall, allowing the villagers to freely explore.
2. They have temporarily turned invisible. There are a few bugs in earlier versions where mobs have been known to disappear and reappear randomly. Although this is unlikely, we don't know your version so we can't rule it out as a possibility.
3. They have entered a Nether portal. If you built a portal in the structure they were in, they might have ran into the portal and been teleported to the Nether.