Let's start with a question. Is defeat something that is defined subjectively or objectively? Is defeat a state of mind or is something that can be determined based on the facts surrounding a particular person's situation? If we define defeat objectively, then the characters in Endgame are utterly defeated. Their situation is hopeless; they will die in Hamm's house or nearby, and there is no sign that there is another life to come. Yet, if we measure defeat subjectively, then most of these characters are not yet defeated, if only because they do not know how to accept defeat and to recognize it. Now, is this refusal to admit defeat just a lack of common sense or is it something like a triumph of the human spirit?
In the play, defeat is something that has to be performed because it cannot be experienced directly. Hamm, in particular, is constantly acting out his own defeat in an effort to make it real.
The characters are not defeated in the play. Despite the apocalyptic setting, defeat is a state of mind and they are not defeated until they give in to death and decide with certainty that their lives are completely devoid of meaning.