Nahiri heads for the Singing City, whose focal point could carry the Core's power through Zendikar's leylines. Jace follows and establishes an uneasy truce: they should understand the mechanism before using it. He is drawn both to Nahiri's vision of stability and to the possibilities of a powerful artifact.
Nissa arrives with Ashaya and other elementals. The confrontation exposes the limits of Jace's mediation. After asking Nissa to trust his wish to take the Core to Ravnica, he tries to take control of her mind. Nissa breaks the mental connection and orders Ashaya to hold him down. His attempt to impose a decision cannot be mistaken for an impartial peacekeeping role, even though he is trying to prevent another catastrophe. Nahiri treats her memory of Zendikar as authority to reshape it; Nissa treats its present life as something that must be heard. The artifact becomes more than the weapon either initially imagined.
When Nissa listens, Zendikar speaks through the Core. She uses it to undo damage rather than enforce an ancient design. The release destroys the Singing City and nearby forest, briefly making the result look like another disaster. Then the elementals rise with renewed strength, new growth appears and the blighted land begins to heal.
The Core falls inert. Nissa returns toward Bala Ged with a confidence built on her own relationship with the plane, while Jace recognises his mistakes. Healing has come with destruction and has not restored everything lost. The important distinction is that Zendikar keeps a future beyond any one guardian's preferred image of it.