Maybe the “undoing” is undoing Rumple’s desire to die for penance.
I was actually thinking that his “undoing” had more to do with the fact that Henry is the motivation behind the selfless acts of his family. Neal’s motivation for sacrificing himself for example – He let go of Emma’s hand and fell through the portal because he didn’t want Henry to lose both his parents and grow up the same way they did. In a sense, Rumple losing Bae again was because of Henry.