Stranger Things season 4 to answer, and the biggest one is about Hopper’s fate. The mid-credits scene in the final episode has made many fans believe that Hopper survived the events at the Russians' underground lab and is now a prisoner in Kamchatka.
Others believe Hopper found a way out at the last second and jumped through the gate and into the clues that point at Hopper not being dead, but where he is and what really happened that night at the lab is a mystery. However, there are some that believe Hopper’s death was all part of a plan to save Hawkins.
Stranger Things season 3 focused on the Russians and their experiments underneath the new Starcourt Mall in Hawkins. Hopper, Joyce, and Murray got too involved in it, with the kids splitting into two groups and dealing with the Mind Flayer and the Russians in their own ways. In the end, Joyce, Murray, and Hopper shut down the lab (and killed a couple of Russians in the process), and Hopper “dying” might have been planned behind Joyce and Murray’s backs.
How Hopper’s Death Was Part Of A Plan
When Hopper and Joyce were still at Murray’s place (with Alexei), they called Dr. Sam Owens for help to take down the Russians’ lab. As he didn’t pick up, they left a message along with Murray’s phone number and continued with their own plans. A theory brought by TVLine suggests that Owens and Hopper came up with a plan to ensure the Russians' operations were shut down without endangering Eleven and Joyce, and it involved faking Hopper’s death. The author adds that, if the Russians believed Hopper was dead, they would have no reason to go after Joyce and/or Eleven in order to stop him from meddling or letting the world know about what they were doing. This is why, in a “blink and you’ll miss it” moment after Joyce turned the keys, Hopper wasn’t where he was supposed to be and his body (or its remains) were never found.
However, there are a couple of things to take into . Supposing Owens called back and managed to talk to Hopper without the rest knowing, it seems very unlikely that either of them would have known how to get out of the lab in case everything went wrong (like, let’s say, a big explosion that turns people into some kind of goo), more so considering they didn’t even know how to access the lab. Something that can the theory is that Hopper was the main target of Grigori (also known as “Russian Terminator” among fans), so it makes sense that he could have made some secret backup plan with someone like Owens. What exactly was the plan and how he could have survived the explosion is unknown, but weirder and more complicated stuff has happened in Stranger Things, and at this point almost anything could happen.