I have a different perspective on this theory.
In S1E1, when the boys are getting on their bikes leaving Will’s house, they talk about how cool Nancy used to be…like the time she dressed up like an Elf for their previous campaign. Mike says, “Yeah, 4 years ago.”
4 years ago would make that 1979, the same year that El sent 001 through the portal opening the first gate.
Coincidently, El opened another gate by contacting/touching the Demogorgon when the boys were playing their DND campaign on November 6, 1983.
So we now have 2 separate connections to the UD portals and the DND campaigns.
I don’t think the Duffers would make it so obvious that this is one big DND game being played by Will, however, I could see the possibility of Vecna using DND as a means to control the real world. The reason Will was kept alive could be because he’s the only one who keeps pushing the group to keep playing. He’s the only one who cares about it.