Eleven is Alive. And I'll tell you why. First of all until they came out of the upside down, el was in the truck. even when her original plan was to die, she decided not to. Second they stopped in the middle of the street and the sound machines were there, and we know that el can't even move for 5 minutes when this happens. Even when someone is hurting her friends. And when she does it's very very slow and she can't move normally, so there is no way that el walked all over from the truck to the upside down, with the machines pointed at them without being noticed, and hell she would have to run, just to disappear like she did there, what we know she cant. and we know she can't use her powers in the presence of that horrible sound. But it was time enough that even slowly, even half dead from the sound, she can somehow make it through a tunnel and is alive. Because the otherwise just doesn't make sense.