When Papa sets fire to his own cotton at the end of the novel, is he acting in a defeated or a self-controlled manner? Is this a moment of triumph or of despair? Of optimism or pessimism?

Papa burns his cotton to distract everyone and save a life. This is an act of heroism and self-sacrifice, he burns his field.... his income to help someone else. It isn't a pessimistic act, though without his quick thinking, there would likely have been a lynching. I believe he is optimistic about what can come of it all when it's over.