New South Wales
There's this in the rules regarding non-player Main Character Strikes:
Rulebook p14 wrote:
If a non-player Main Character draws a
Strike, ignore its text, but if it has at least 1
damage, then they are defeated.
Terrified has no damage, so you really luck out when it hits a non-Player Main Character. You just discard Terrified and that's it!
Edit: And yes, Niska's Revenge can and must target the non-Player Main Characters if they are higher Rank than the Player Main Characters. Note that they lose their Rank while they are defeated, though.