It's possible she could physically be in a coma, but that we'd get to see her "alive" in another dimension/realm. Kind of like she was in Vecna's mindscape. Maybe she's trapped in it, as Vecna's prisoner?
@Fisher Fan - remember what Vecna told El -- (not an exact quote): "They are not really dead - they are always with me in here" (pointing at his head) -- so, is Max with him in his head? And can El find and rescue her?
Well the Duffers did say that his death will have BIG repercussions for everyone involved. So theorize on that the way you will but I think we might get some flashback scenes of Eddie (hopefully)