I didn't change my villagers a lot on my first island. I just chose who I liked and then stuck with them. If someone wanted to leave, and I felt good about it, I would agree to it, but most of my villagers on that island I would now consider permanent residents.
On my main island, I have: Agnes, Louie, Norma, Rhonda, Patty, Goldie, Gayle, Teddy, Megan, and Pinky. Agnes and Louie were my starting villagers. Rhonda was one of my first five. Patty was the first and only villager I've adopted from someone else (she had been gifted clothes too!), and that was in my very early days of playing. Megan was the first villager I found through mystery island hunting.
I would consider Agnes, Louie, Patty, and Gayle to be permanent, though I'm quite attached to all the bears as well. If any of the other residents asked to leave, I would definitely just base it on how I felt at the time. The only time I've come to miss a villager after doing that is with Merengue! I do still miss her sometimes!
On my second island, I allowed everyone to move in randomly. It's definitely been a strange mix of villagers, and I probably wouldn't use this method of finding villagers again. On a positive note though, I did get to meet a lot of new villagers I wouldn't have otherwise chosen to live with. For example, I've come to love Hippeaux on my island! Overall, I think eventually most of these villagers will be replaced! Fang definitely feels permanent on my second island, and I think Stu is quite cute too.
I'm not interested in cycling the villagers out on either of my islands, and I'm not too worried about collecting photos, so I just let them come and go as it feels right.
