Answer:
The evidence that the text shows for Koskoosh's resignation is the physical state he is in.
Step-by-step explanation:
Koskoosh was old, tired and blind. He was not in a position to move on with his tribe, as he would be a burden and end up disturbing the other members of the tribe, who might not even achieve their goals.
In other words, Koskoosh, knew and accepted that it would not be a good help and so he was left behind as his last way of helping his people. He knows that his life is at an end and that his mission is over.