This: I think Elliot and Mr. Robot(his dad) are dead/have been dead. Tyrell has always been a real person. People have always been able to see him. Who is Tyrell? I feel like that's the real question. Also, It would make sense that Elliot's mom had that cassette recorder of him and Darlene as a kid. Why would she? Because he died when he fell out the window. That was my crazy speculation for the day. I liked this episode.
It could also be that a time machine did exist and Elliot has been trying to stop it ... like Terminator.