Obviously, in retrospect we all know it was Rumplestilskin's sacrifice, but this is what I was anticipating when I first watched.

I also thought that it might have referred to an emotional undoing.

^An emotional undoing is a theory I came across on another fan site, but I never thought of it myself. Another form of emotional undoing they suggested is if Rumplestilskin attempted to kill Henry to protect himself, but Neal caught him and he lost Neal's forgiveness for good as a result.