I wouldn't necessarily say any of current villagers are permanent, but Zell is probably pretty close. I don't care much for many of the Smug villagers, so getting Zell as my first camper was great. There's only like 2-3 other Smugs that I'd choose to let replace him.
Butch is also close to being permanent, he's just such a cute doggo. There are other Crankies out there I like more than him, though, so it all depends on who shows up to the campsite and which other villagers I have available to leave (I keep at least one of every personality, and I must have their photo before they can leave).
I've wanted an Octopus ever since Wild World, and I finally got Marina this time. I'd like to keep her around, but there a lot of other nice Normals out there and it's not one of the personality types I like to double up on. So again, it'll depend on who shows up at the campsite. Like if Molly or Merengue show up, she's outta here, lol.
I still have Tank from my original 10, but that's mostly because he's never asked to leave and the campsite hasn't provided me any great Jocks yet. I do like him though, so it'll be a little sad to see him go when the time comes.
My other current residents, Tangy, Drago, Annalise, Curt, Huck, and Diva are all expendable. Diva will have to wait until a good Sisterly shows up in the campsite, though. I don't like many of them, and back when I let Canberra move out on her own, I wasn't even able to find a replacement Sisterly with Nook Miles. Went to a ton of islands, didn't find a single good candidate, and ended up having to choose a different personality because I ran out of time. I'm not too keen on doing that again, lol.