Won't be the same...

I think that's why the tagline was something like "the summer that changes everything." It was talking about Hopper's death and the Byers and Eleven moving away. It's time for all the characters to adapt and stuff to Hopper no longer being around and will have to figure out how to do things without them. The viewers will also have to adapt to him being gone. Also, it's a change for the four main boys since one of them moves away. Eleven goes through a change too because she loses the two most important guys/men in her life. At least Mike is just temporary and she'll get to see him sometimes. They'll be seeing each other at Thanksgiving and Christmas time though according to their dialogue at the end of the season, but that'll be off screen and the viewers/fans won't be able to see it. But something will go down in Season 4 to bring all the characters together again. Actually, I don't know why Jonathan couldn't stay or Nancy couldn't go with. I believe the two are 18 or older now and out of high school. They can do whatever they want. Maybe Jonathan feels he needs to be there for his mom and help out and help her with Will. But Nancy could've maybe tagged along. Or Jonathan or Nancy could've rented an apartment or something close to Joyce, Will, and Eleven. That way Jonathan could be there if Joyce needs him to drive Will to school or pick him up. But Jonathan and Nancy are the only ones I questioned why they (the writers and everyone behind the camera) chose to separate the two because of the move. They are adults now. But yeah. I think they weren't messing around with the season's tag line. It definitely means change for the show. For both the characters and viewers.