I've noticed a tendency for villages to become ghost towns eventually. I set myself up to observe a village from the air in creative mode. Several hours later, I noticed the village had no villagers.

I had observed zombies hanging around doors of buildings that have villagers inside. In the morning when the sun rises, the zombies are protected by the roof overhang. If I break the roof overhang (perhaps especially because I did this), when a villager opens the door to leave the building, the zombie slips inside and becomes protected from the sun.

I suspect the village becomes a ghost town because the zombies who slip indoors can stay indoors all day long and kill villagers as they enter the buildings again. Eventually there are no villagers left, and some of the buildings have zombies, drowned, and zombie villagers inside who can't get out.

Is there any way to ensure that the village can sustain itself? I don't recall zombies hanging around village doors all night pre-1.11.