Oldboy... What do you think happened at the end?

Obviously you can tell this is a spoiler-heavy thread from the title, so I'm not going to bother using tags.

Anyway, remember the scene right at the end where Oh Dae-su gets hypnotized, and he's split into two people, himself and The Monster? The hypnotist says the monster will walk away, and by the time he takes 50 steps, he'll die. Keeping in mind that she said it was risky and mightn't work, then when Dae-su wakes up, the camera pans out and we can the footprints in the snow.

The film leaves us with no answers as to whether the hypnosis worked or not, but what did everyone else think? Was it the monster that survived? Fantastic way to end the film though, the way he smiles just had me thinking.