Board Thread:General Discussion/@comment-26513870-20150622055620/@comment-24674051-20150622155742

In response to the thread, I would imagine that the Darkness would stick with Rumple, and eventually fill his heart with Darkness, just as it was doing anyway. The point of the spell was not to release the darkness, but to break the control of the Dagger over the darkness. Based on what we know of the Dark One curse after the season Finale, Merlin captured the darkness and bound it to a human soul in order that it could be controlled with the Dagger.

A little speculation here is that Merlin originally kept the dagger, but somehow one of the dark ones (probably the original one) managed to gain control of the dagger, and thus the ability to control their actions. Over the years, the dagger has changed ownership as the curse of the Dark One passed from one owner to another. Each Dark one probably maintained just enough humanity to be able to pass the Dark One along to a new host as they were dying. Rumple, though, was not about to let go of the power of the Dark One, and as a result, he was almost completely overcome by the darkness.

A side question: what did the heart of one that knew him prior to becoming the Dark One have to do with seperating the Dagger from the equation? Or was that just a red herring that Ingrid threw in so that she could get what she wanted?