I don't think it's even possible to destroy the Sith anymore. Not after the shit that went down at Mortis, according to Luke after Abeloth's (temporary) defeat. Apparently, with the Daughter and the Son dead, the Jedi and the Sith had become the respective embodiments of the Light and the Dark. It's quite possible that the Force itself will ensure the survival/resurrection of the Sith if the Jedi ever succeed in wiping them out to keep the balance, and vice-versa.
Not to mention it'd be a complete disaster. Remember: while it might be otherwise in canon, in Legends, it is explicitly stated that the ultimate victory of either Light or Darkness would only result in devastation for the galaxy.
Despite what Lucas might say, in Legends, balance is the textbook/Taoist definition, and not his or Disney's repeated
tantrums statements that balance requires the Dark's complete destruction. Everything comes in twos: Light and Dark, Life and Death, Wisdom and Power, Peace and Passion, Creation and Destruction, even Good and Evil if you want to mince words.
Ironically, the pre-Great Sith War Jedi acknowledged this, with the original version of the Jedi Code.
Ignorance, yet knowledge.
Emotion, yet peace.
Passion, yet serenity.
Chaos, yet harmony.
Death, yet the Force.
It was only after the Great Sith War that they began rejecting the concept of duality, passed down from the ancient Je'dai, and grew increasingly dogmatic and absolutist in their philosophical interpretation of the Force. Though even then, their understanding of duality was...inferior (?), compared to the Je'dai, as seen in their code.
There is no ignorance, there is knowledge.
There is no fear, there is power.
I am the heart of the Force.
I am the cleansing fire of the Light.
I am the mystery of the Darkness.
In balance with chaos and harmony,
Immortal in the Force.
The duality is so present in the Je'dai's teachings that they simultaneously reject (as shown in the first two lines) and accept (as shown in the fourth, fifth, and sixth lines) the concept of duality.