How did each of the Guardians die?

Infernacus – Athrenna took him on herself and tore out his throat. Athrenna also killed Nydia shortly after.

Volga – Was torn apart by the Silverwings while trying to lead the children and young dragons out of warfang. She was torn apart for having horns mocking Kuronium in the Silverwing’s eyes.

Klaudious – Child Feuriah led the Silverwings to him to distract them so Ignitus could sneak the children out of Warfang in Volga’s place.

Acerbus – Decapitation by Feuriah’s own Rolling Tail Strike attack to prove her loyalty to the Kuros.