She’s alive. She didn’t use a blindfold when saying goodbye to Mike in the pitch black water while they all see her “about to sacrifice herself” she was already somewhere else with the blindfold on saying goodbye running away using Kali’s powers to make everyone believe she died just like when Hopper accidentally shot her he believed it and saw blood. Happens to Kali also. She knew Hopper would never let her go so she felt this was the only way so the government/military would stop coming after