If it turns out that Sara is alive somehow, thats should be the only way she makes a return. Everyone else on the list died on screen, so they are confirmed deaths.
I don't think the Mind Flayer can control things that are already dead, because then any deceased character could technically come back. It appears that the hosts need to be alive at the time, when they are taken over, otherwise the Mind Flayer could have just made some zombies from all the folks buried at Hawkins Cemetery. The Flayed where mutated by chemicals, so the hosts were technically somewhere between alive/undead.
When the Gate is closed the hosts appear to die, like the Demodogs and Flayed Spider Monster, because they are severed from the Mind Flayer's control. That's why Joyce, Nancy and Jonathan where trying to get the Mind Flayer out of Will's body before the Gate was closed. However we never knew if that was entirely true, as the Demodogs could have been just unconscious and the soldiers could have shoot them to ensure they did not wake up.
The same could be said about the Flayed Spider Monster, who was made of host bodies, but its difficult say for certain whether the FSM could be conscious without the Mind Flayer, because the host minds where detached from their bodies. Regardless the FSM would have been burnt by the army, so that solves the issue of it returning.
This could therefore explain how the Russians had a Demgogon, if it was captured or created, because the Demogorgon could possibly survive without being connected to the Mind Flayer, after the Gate was closed a second time.
