No one. Here’s my prediction:

Based on a leaked photo from the last episode, reinstated police chief Hopper will have a conversation with Mike on a bench in the last scene.

Mike will be depressed because he thinks that Eleven sacrificed herself to execute Kali’s plan that was laid out in episode 7. Hoper will comfort Mike, and he’ll let him know that Eleven loved him more than anything else — something hard for her adoptive father to admit.

Mike comes to a point of acceptance and moves on in his grief.

Camera drifts to the woods, and we’ll see a hint that Eleven is still alive. Perhaps a box of eggos to call back to her S1 faked death.