A new theory from Dungeons & Dragons lore suggests that if Vecna (Jamie Campbell Bower) dies in season 5, Will Byers might die too.
In the first episode of Stranger Things, Will Byers is abducted and taken to the Upside Down. He manages to escape but the horrific experience gave him a psychic-like connection to the parallel dimension. He has the ability to see and feel what the Mind Flayer saw and felt. He feels a strange sensation on the back of his neck, whenever an Upside Down monster was close.
Season 4 revealed that Will’s connection is to Vecna, who created the Mind Flayer. In the season 4 finale, Will returns to Hawkins and can once again feel Vecna’s presence, sharing with Mike Wheeler, “I can feel him, and he’s hurt. He’s hurting. But he’s still alive… And he’s not going to stop. Ever… We have to kill him.”
Now in D&D, Vecna is able to rip out his soul and put it in a horcrux-like object called a phylactery. To kill Vecna, this object has to be destroyed. In season 4, Vecna manages to survive multiple attacks which hints that he exhibits similar immortal-like qualities. However unlike any object, the Demogorgans, Demodogs, Demobats and Mind Flayer – act as his phylactery. These other things must be destroyed to defeat him completely. As the season 4 finale hinted, Will is still connected to Vecna’s hive mind, so if Vecna dies in season 5, Will might too.
It seems that the only way for Will to be saved is if Vecna himself casts him out of the hive mind. In season 2, Will’s connection to the Mind Flayer allowed him to see and feel Vecna’s thoughts and movements which allowed him to identify the Upside Down tunnels located beneath Hawkins. The season 4 finale has hinted that this power seems to have returned allowing Will to spy on Vecna’s actions, helping Hawkins gang to stay one step ahead of him. If this happens, Vecna might have to sever his connection with Will.
Additionally, Will Byers might have to sacrifice himself to defeat Vecna. But there is a possibility that he could return as Eleven has the power to revive. Eleven rescued Max Mayfield using her supernatural abilities to revive her from the dead. Thus if Will must die to kill Vecna, Eleven could potentially revive him afterwards.