Peril was getting erased from existence by the explosive power of Leon Chronos, the Dragonborn. And although Peril cannot truly die this way, coming back to life would be no easy feat.
The source of a Great Demon's immortality is in their Territories. A Territory is a dimension of magic which fuels a Great Demon's incredible power, and also grants them immortality. This allows them to come back to life many times over, even if their body is completely destroyed. But there are some attacks that are just too much for a Territory to handle, and Great Demons tend to be careful of these kinds of attacks.
The Erasing flame erases everything it touches from existence, and Peril does not want to find out how long it would take for him to come back from that.
Peril: Not today. (Peril thought as he teleports away from the suit of armour, just before it is completely incinerated by Leon's erasing flames)
