This has been a nagging question for a while, would one prefer to theorize that Sunset would return to Equestria or live out the rest of her life in the human world?
Personally, I theorize she'd live the rest of her life in the human world considering the close bonds she has with the Rainbooms and everyone in the human world and it'd be pretty disappointing and sad if she ended up leaving them in the end for Equestria. Especially considering she didn't really have much a connection to anyone in Equestria aside from Princess Twilight and Princess Celestia (and later Starlight Glimmer in Movie Magic) so it feels like it'd make more sense for her to live out the rest of her human life in the human world, occasionally using the portal to visit Equestria once in a while and communicating to Princess Twilight via the journal.
As for what she'd do for a living as an adult, maybe she'd eventually become the principal of Canterlot High after Celestia retires (paralleling Princess Twilight succeeding Princess Celestia as ruler of Equestria), inspiring students into their own friendships for the next generations.
I personally doubt they would've actually had Sunset leave the human world for good and cut off all contact with her human friends if they had gotten Equestria Girls a proper finale. I doubt they'd spend several movies, specials, and shorts focusing on the girls' friendship if Sunset did get permanent separation.
Heck, Forgotten Friendship even has Sunset get her memories of the human world back immediately after they're removed so that does imply to me that they wouldn't go for her cutting contact with the human world. Especially when we have pony Twilight still being in contact with the rest of the Mane 6 even when moving to Canterlot as princess.
The deleted homesick plot in Friendship Games also ended with Sunset choosing the human world over Equestria.
I think even one of the writers mentioned Sunset's true home is the human world, so I'm positive she'd spend the rest of her days there (maybe becomes a teacher at Canterlot High) with occasional visits to Equestria and using the journals to message Twilight and Celestia.