Despite having quite a few amiibo cards of my favourite villagers; it's never easy when they want to move off the Island. I do generally allow it to experience newer villagers. Ones I've never had before.
Heck, Julian is my one fav but I never had him until I gave him a go on New Horizons. So it shows, that even though it's sad saying goodbye, it's more see you later, so you can experience and love more villagers, and be able to bring them back easier this time around in the game.
I love Vivian, but I know that I would love to try out more people, so, until I get her villager photo; she's all good on leaving. I've made her house nice too, I did a pretty good job on it, and wouldn be nice to give her away~
I feel like the only one, now that I think about who can't leave is Nan. I was going to say Julian too, but I haven't done as much with him recently, and I would hate for me to feel bored of him.
That's another aspect, if they're there for WAY too long, and I am not almost feeling the same spark seeing them all the time, I'll accept they need to go. Not in a bad way.
See, what happen in New Leaf, is that I had Carmen in my town FOR YEARS. And she would hardly ever leave FOR YEARS. I loved a lot of my villagers, but whenever I saw her, I just got bumped out. Because she was there for so long, I didn't feel any connection to her, and was just dying for her to leave.
In New Horizons, I almost had that feeling with Daisy, despite loving her. So when she wanted to move, I said sure, because I didn't want the Carmen scenerio to happen again~!
To have another Island/switch would be amazing, because I can try out new themes with different villagers. And when I do that, I have a better idea what other villagers I like, who I've never tried before~
(Still waiting for Diva to show herself on a villager hunt, but she hasnt yet!)