I had my first Marshal (the one my friend gave me) for two years. I kicked him out and used his amiibo card to make him original again once the update came out.
I think that Cole has lived in my new town the longest of any villager. He's lived in my town for about 2 years.
In my old town, I still had Timbra and Brocollo, who were both my starting villagers. I would have still had Rolf had I not recklessly time traveled...