well all through the movie it was implied that tyler durden was imagined by norton's character all along. aka he had schizophrenia. this makes sense because the movie takes place mostly in first-person from norton's character's point of view.
so basically what that means is that tyler durden never existed- everything tyler did was actually his doing.
and that would explain the scenes around the end where you see him getting beat up by tyler in the basement parking lot when on the camera theres nobody beating him up- its because he's imagining it.
its confusing yes i know and it certainly doenst explain everything but thats what i see