Well, Gellak the Half-Orc Bard kind of inherited the sword after his friend, Durrash, killed the previous owner and then inconvenient-like got himself killed defending us from a dragon.
The thing is this: Gellak is a good bloke, and knows that the sword is neutral evil and (at least in our version of this world) is determined to kill neutral good beings. Now, Gellak can't go along with that — he's chaotic good.
His first thought was to destroy it using Dispel Magic: this would, with a good enough roll, would seem to provide a means to eliminate the evil weapon, preventing it from doing its dastardly deeds via Gellak or anyone else.
However, the best move, considering the rarity of such powerful items would be to find a way to change the alignment of the sword.
Yes, this will probably turn into a quest, but the DM sent me to the Waterdeep Archives and libraries looking for answers, giving me a chance to come up with a plausible solution.
What are the known (or logical) ways to change the alignment of a legendary item in a 5e campaign? Who would be the people in Waterdeep that might have answers to this question if you, Oh Wise Sages, do not?
Best Answer
"Sentient magic items function as NPCs under the DM's control," says the DMG (214). They have their own personalities; they have Intelligence, Wisdom, and Charisma scores. If they weren't trapped inside swords and boots, they'd be out living their lives and making decisions just like everybody else.
The PHB (122) says celestials and fiends are locked into their alignment, but "for many thinking creatures, alignment is a moral choice." Even the races created by evil gods have free will, and can pursue good alignments if they choose.
I gather that HotDQ isn't very specific about Hazirawn's personality, but if there really is a sentient being in there, you should be able to change its alignment the same way you'd convince a wrathful orc or bloodthirsty gnoll to turn toward Good. It could be a philosophical argument, or a series of object lessons that show the sword the error of its ways. Your chances of success would depend on Hazirawn's own force of personality, which is why I brought up that Charisma score.
Although RAW implies that people can change their alignment, it's up to your DM whether they actually can, and whether an outside agent can impose that kind of change. In any case, my answer is that a sentient magic item, by virtue of possessing a personality, should be treated like a person.
(If you can't hack the philosophical argument angle, you might try to get Hazirawn to draw Balance from the Deck of Many Things...)