Q: If my Ariana, Young Prodigy were to be destroyed by damage, can my Kala, Trusty Companion be destroyed instead?
A: Technically, yes. You may still use Kala’s ability to destroy him instead of Ariana. However, Ariana would still have the damage on her, and she would be destroyed (again) before moving to the next priority sequence. (See Game Mechanics Damage – 10.2)