Why does Chauvelin have to die at the end for there to be a successful resolution?

Chauvelin, the novel's chief villain, is a French agent who has English diplomacy rights. He is in England looking for the Pimpernel and anyone else who is attempting to rescue French aristocrats. His 'hard-hearted, vengeful' nature contrasts with the dashing Pimpernel. So Chauvelin personifies the forces that seek to destroy our protagonist. This becomes a "good" vs "evil" motif in which, if the protagonists triumphs, the antagonist must be vanquished.