Board Thread:General Discussion/@comment-26901329-20150728204029/@comment-27934866-20160503171246

True Love's Kiss can break the Dark One's Curse, but it will have no effect if the Dark One in question likes the power they've been betrothed with and don't want to give it up e.g. Back in Season 1 when Belle and Rumplestltskin shared True Love's Kiss it was capable of breaking the Dark One's Curse, but he chose power over love. In logical terms if the afflicted person wants the power it's no longer considered a Curse. The only real part of being the Dark One that's a Curse is the Dark One's Dagger.

If the Dark One is killed without the Dark One's Dagger, the person in question will expel the power of darkness, with no new Dark One, and the Curse will "pass from this world".

The Dark One cannot die from their heart turning black, but the host it's tethered to can leaving only The Dark One (and nothing of the human host) behind. When the Apprentice extracted the Darkness from Gold's heart and tried to trap it in the hat, once it got loose this allowed it to roam around of its own free will to seek out a new host.

The Darkness is immortal, but OUAT's interpretation of immortal is that one can live forever, but it doesn't mean they cannot die.

IMO the most effective way to get rid of the Dark One's Curse is to kill the current host without using the Dark One's Dagger so the powers of the Dark One will be expelled from this world without anyone else being next in line to inherit it. Another effective but more dangerous method would be available after the hosts heart has turned black, use the Dagger and command the Dark One to cross the Storybrooke town line due to the fact there's no magic beyond that point and due to the host body being dead, the Dark One will die without being stabbed by the Dark One's Dagger.