Though there were a lot of heartbreaking moments from Avengers: Infinity War. One of the most effective was Vision's death. Not only did Wanda have to kill him to prevent Thanos from getting the last stone, but she then had to watch as Thanos brought him back only to kill him again.
Unlike some of the other deaths in Infinity War, Vision was not brought back in Endgame. However, with the WandaVision series coming, we know he will return in some way, but for now all we have are speculations. Here are some of the best theories about how Vision will com back for WandaVision.
Recreating The Vision
Vision is a very complex character and his origins reflect that. He is partially the Jarvis AI program, part the creation of Ultron and part the Mind Stone. All these factors came into play to bring the android to life, so if Wanda could find a similar method, she might be able to recreate him.
She would need the help of some of the greater scientific minds in the MCU, and with Tony gone, that would leave Banner as the most likely one who could help her as he had a hand in bringing him to life in the first place.
Multiverse
The multiverse is a new concept apparently being introduced to the MCU in Spider-Man: Far From Home. Going by the trailers, Mysterio seems to have some connection to the multiverse as he claims to come from another world.
There are still a lot of question surrounding the idea of the multiverse, including whether it actually exists, but it does open up the possible return of certain characters, including Vision. The new series might find Wanda traveling into a new world in search of an alternate reality where Vision is still alive.
Doctor Strange
There are few characters who could plausibly play a role in bringing Vision back, but Doctor Strange is certainly one of them. With his endless and complicated set of powers, it's not crazy to think he could have some connection to characters who have died. Even more important is his connection to the Time Stone.
If Captain America returned all of the Infinity Stones to their rightful place at the end of Endgame, Doctor Strange should theoretically have the Time Stone. Since it brought Vision back from the dead the first time, it could conceivably be used again and maybe Strange knows how.
Set In The Past
While not the most complex or inventive solution, the easiest solution for how Vision will return seems to be that the series is simply set before he died. When we see Wanda and Vision in Infinity War, they are both in hiding having fought on opposite sides in Civil War.
The series could take place between these two movies, showing them meeting in secret and developing their romance. It's unclear if they got up to many adventures in this time period, but the series might just be a quiet love story.
Time Travel
Now that time travel has been introduced in the MCU, it feels a bit like it can be constantly used as a solution to our heroes' problems. While they will have to develop some way to explain why the remaining Avengers aren't constantly using the technology, this might be the solution that brings Vision back.
It's hard to imagine that Wanda wouldn't at least try using the new tech to get him back. It could be that she uses the time travel method only for things to go wrong and thus ending it as a plot point for the future of the MCU.
Shuri
When it was discovered that Thanos would come for the Mind Stone, the Avengers devised a plan to separate Vision from the stone and thus save his life. In Wakanda, Shuri seemed to have found a way to achieve this but was unable to complete it before Thanos' army attacked.
Though Vision is dead, it's possible that Shuri found a way to have him live on without the stone. Therefore, he could be brought back with the mind of Jarvis. If anyone can figure out a way to do this, it would be Shuri.
Wanda's Powers
To say that magic can bring Vision back seems like a cop out but there is a decent explanation for how this can actually be the case. Wanda's powers are a bit difficult to define, but they seem to be magic of some sort what comes from the Mind Stone.
Seeing as they both come from the Mind Stone, it would make sense that Wanda could use her powers to resurrect Vision. His body remains, just without the Mind Stone, so it is possible she contains some of the power that gave Vision life in the first place.
Infinity Stones
It seems like the Infinity Saga is finished in the MCU, which probably means the Infinity Stones won't play a big role going forward. However, the stones seem to be so important for both the Wanda and Vision characters, it would make sense they come into play in their series.
As already explored, the Mind Stone and Time Stone have played significant roles in their stories. The Soul Stone seems to have a connection to the after life. The Reality Stone seems to mirror Wanda's powers in many ways. The Space Stone could link to the multiverse. It seems like the stones could still hold the key to Vision's return.
Wanda's Connection
The last thing Vision says to Wanda is "I just feel you", a reference to their connection from the Mind Stone. However, that line could have more meaning than we initially thought. The confirmed title of WandaVision seems very odd, but might also reveal something about the direction the series will go.
The connection between these two could be strong enough that part of Vision remains within Wanda. It could be that Wanda is able to communicate or envision him like a voice in her head. Maybe this could lead to her somehow bringing him back in physical form as well.
New Vision
Even before he was Vision, Jarvis was nearly killed by Ultron. He only managed to escape by copying himself onto the internet until Tony could find him and put him in the body of Vision. It is possible that Vision did the same thing before being killed by Thanos.
Maybe Vision's mind is floating out their scattered on the internet, slowly piecing itself back together. The series could find Vision trying to communicate with Wanda as they search for a way to make a new Vision for him to embody.