Is hopper alive? How about Alexi? Or Billy will return to join the squad? Lets see!
Theory 1 : Hopper is alive?[]
We seen on the post credits scene on of the guards of Russia said, "No, not the american." Could be Hopper. All we know of evidence is just this post credit scene.
It was revealed on a video called Love From Russia that Hopper was alive and has been working as a prisoner for the Soviets.
Theory 2 : Steve will die?[]
We don't know why we explain this theory. In stranger things 2 we seen a scene Steve using as bait. If we have a rate of 90% Steve is alive and ready for season 4.
Theory 3 : The Upside Down is the future of Hawkins[]
David Harbour answered that the Upside Down is the future of Hawkins in spring. Can they destroy the gate once and for all? Some of the fans said no. SIKE. It's possible Hawkins will be wasteland full of demodogs and the ultra demogorgon in Russia.
Theory 4: Will Eleven and the Byers move to Salt Lake City, Utah?[]
At the ending of The Battle of Starcourt(the finale of Stranger Things 3), Eleven moved to live with Joyce and her sons, Will and Jonathan. The family made plans to move away from Hawkins, leaving all their friends behind, but still contacting and visiting them in the future.
If they move to Salt Lake City, they might get a chance to meet Suzie(Dustin's girlfriend), who had a small appearance in season 3. Maybe Suzie could get a major role in the fourth season, just like Erica Sinclair got a larger role in the third season.
Theory 5: Will Kali return?[]
Kali and her fellow gangsters were never seen nor mention in ST3. They were last seen escaping in season 2 where they can find another sanctuary from the police. She and her friends might return after a season 3 absence.
Theory 6: Will Eleven's powers come back[]
Eleven's powers were severely weakened after the Mind Flayer bit her. Eleven may go on a journey to find a solution that can restore her powers.
Theory 7: Is the Russian Demogorgon the same one from the first season?[]
In the end of season 1, Eleven used her first full strength to stop the demogorgon who killed Barbera and abducted Will. El's power made her and the demogorgon vanished out of the sight. Eleven survives and wakes up in the Upside Down where she sees a gateway back to Hawkins.
In the post credit scene, a prisoner is killed by a demogorgon in Russia. Could it be the same one in ST1? Eleven may had defeated the monster and saved Hawkins, but she probably didn't killed it. The monster may had been transported far away in the Upside Down version of Russia and found a gateway there. The Soviets must've captured the demogorgon and kept it as an experiment of the living.