Are old villagers that have left able to return to your village, and visit you? I was watching a Linandko video, https://www.youtube.com/watch?v=jeY5B12dgfU&list=PL6KjQD8nI9QbAfJAcAfW6tvHVQa-yikLi&index=56 at about 13 minutes, Lindsey says 'You always have your old villagers visiting you."
How does this work?
Once a certain amount of villagers have moved from your town, -I think it might be three- the first villager to move out will visit pop up in your mall. Each time a villager moves out, an old villager will appear in your mall and they will do so in the order that they moved out in. Even if the villager moves to another town, they will still appear in your mall.
Old villagers can appear in Nooklings, Club 444, Able Sisters, Museum exhibits and the main mall area.