What plan do the patients hatch for mcmurphy? why does he refuse for the time being? How does this add to our understanding of his character and motives?

The men hatch a plan for McMurphy to escape from the ward on Saturday night. Mc Murphy postpones his departure to comfort Sandy. 

McMurphy’s delay in leaving the ward is an ambiguous event, for although he ostensibly makes a small error by falling asleep, the event is perhaps too convenient. Given the signs of his martyrdom, there is a strong possibility that McMurphy never intended to leave the ward and that his actions are a form of self-sacrifice. There are many reasons for him to go, but there are also important reasons for him to stay.