Just how many ways are there to destroy the DO permantly without becoming the DO yourself? We all know about the squid ink. But I think that I have discovered another way, in 416 Rumple steals a potion from the fairies that can temporairily undo any spell, the reversal potion, Rumple uses it to turn Agust back to wood. Being the DO is a curse, so maybe this can also temporairily be broken and if it is you can kill him without being the DO, even though Rumple said it could undo spells for a brief moment, not curses. I also thought of the true love potion, being the DO makes it hard to truly accept love (At least I think.), so maybe by drinking the true love potion you can brake this curse. Rumple said it was able to brake the sleeping curse, the product of true love was able to break the DC, so maybe it can break the DO's curse. Even though, it is pure darkness we're speaking of, maybe there is something Merlin has to destroy it, maybe the excalibur.
Thoughts??