Sunny knew what was supposed to happen.
In fact, it was very simple — the answer was nothing.
Mordret's Reflections were strange creatures, after all. They were neither dead nor alive, neither divine nor profane. A long time ago, when he killed the Mirror Beast on Reckoning Island, the Spell had announced the kill, but did not whisper anything about his shadow growing stronger.
Sunny was banished from the Nightmare Spell now, but the result would be the same. Killing Reflections did not grant him fragments, and no shadow would appear in the silent stillness of his soul.
Therefore, Saint was unlikely to receive any reward for slaying the Supreme Reflection, either. Even its darkness was merely a reflection of Revel's own — now that the living mirror was gone and there was nothing left to reflect it, the false darkness would most likely disappear, as well.