I was playing on a world with the seed 109774369 which has a sky island after curing a zombie villager on the island and switching it to peaceful for a couple days and then switched it to medium the first night after circling the building fisherman was in and then going to help my friend on the ground. In the morning the villager was gone. the island was fenced so he couldn't have fallen off and he was in an iron door home so he couldn't have gotten killed.