Whether you loved or hated the finale, it's hard to argue that it didn't close every chapter opened at the start of Stranger Things. However, that doesn't mean that we'll never see demogorgons, alternate dimensions, or nostalgia again as we're going to get multiple projects from Stranger Things in the future, including a spin-off series which apparently has links to one key scene in the finale.
Speaking with Variety, Matt and Ross Duffer explained that the scene involving a young Henry/Vecna and the stone in the briefcase will be very important to the spinoff. "The spinoff is going to delve into that and explain that, and you're going to understand it. But it's a completely different mythology. So it's not a deep exploration of the Mind Flayer or anything like that. It's very fresh and very new, but yes, it will answer some of the loose threads that are remaining," Matt Duffer said.
The Duffers are continuing to work on the Stranger Things spinoff, but it might look like quite a different show to the main series. "We're actually really excited, and it's very exciting to work with a clean slate: completely new characters, new town, new world, new mythology," Matt added.
The Duffer brothers won't be acting as showrunners on the spin-off, but seem like they're heavily involved in the writing and creative processes of it. We'll have to wait and see what else this IP can bring as people recover from the decade-long story they've just seen close.