Eleven was one of the most compelling characters to come out of Netflix's Stranger Things, and a lot of that was thanks to actress Millie Bobby Brown's performance. Eleven definitely made her mark on the viewing audience (the sheer number of Elevens running around this Halloween can attest to that) because of her mix of power and vulnerability, and the desire audiences had to see her escape her painful upbringing and find a little happiness. That didn't quite happen for Eleven in Season 1; instead she ended up using one last jolt of her superpowers to get rid of the monster tormenting everyone, which made her disappear in the process. But luckily Eleven will return to Stranger Things Season 2. The only question is how.
Though Eleven left no trace behind when she and the monster blinked out of existence, there were hints that she wouldn't be gone for good. When police chief Jim Hopper left her favorite snack (Eggos, obvi) in a box in the woods, it became clear Eleven was still out there somewhere. It's possible she disappeared much like Will did at the start of the first season, and she's now trapped in the Upside Down just like he was. The circumstances of her return remain uncertain for now.
Despite the clues in the finale that she might be back, showrunners Matt and Ross Duffer have played coy about her return. Though they confirmed to Entertainment Weekly that everyone would be coming back for Season 2, when asked about Eleven specifically, Ross Duffer said, "We don't know about Eleven. We leave that up in the air."
In fact, there still hasn't been an official confirmation from the Duffers or from Netflix that Eleven will be be back; when TVLine reported the news they merely cited "sources" as having provided the info. However, the Duffer brothers did say that they planned to delve deeper into the show's mythology in Season 2 and explore the Upside Down even further. According to them, the gate between worlds is still very much open, which bodes well for Eleven's ability to return – if she is indeed in the Upside Down.
It's understandable that those behind the scenes would rather keep the future of Eleven's journey under wraps to maintain the mystery, but even without knowing the details it's good to know she'll be back. Stranger Things wouldn't be the same without her.