The orthon‘s statblock states, "When it is reduced to 15 hit points or fewer, the orthon causes itself to explode." (Mordenkainen’s Tome of Foes p. 169)
On the one hand, 0 HP is fewer than 15 HP. On the other hand, Explosive Retribution is listed under "Reactions," and you can’t take a reaction when you’re dead.
Is reducing the orthon from 16+ HP to 0 HP at once an effective way to prevent it from using its Explosive Retribution?