So you get a critical strike from yor opponent and and when making the fittnes check you use Opportunity to Inflame another character in the scene with your presence, causing them to receive 2 strife. (Table 8-1, pag 329)
That strife puts your opponent Compromised so
So you "may" do inmediatly an attack action to inflict a critical strike agains your foe.
This action is resolved before the resolution of the initial interrupted critical strike of your foe.
This assuming any of your checks generate enough strife to get you Compromised. Otherwise your opponent interrupts your finishing blow and resolves it before yours.
If the Duel was to first strike or first blood the duel ends here (unless the oponent is eager to loose honor)
If the combat was to death; Either if the opponent dies or not the original Critical strike resolves because was interruppted in the middle of the check. Whith the posibility of kill you too.