At one point McMurphy decides to fall in line when he learns his stay in the ward is indefinite and his release is solely determined by the Big Nurse. As a result, Cheswick drowns himself in the ward's swimming pool when he decides he himself will never escape the relentless Big Nurse.

Why and how does Cheswick die?

Charles Cheswick

The first patient to support McMurphy's rebellion against Nurse Ratched's power. Cheswick, a man of much talk and little action, drowns in the pool—possibly a suicide—after McMurphy does not support Cheswick when Cheswick takes a stand against Nurse Ratched.

Does Cheswick kill himself in the movie?

The film employs the initial altercation between McMurphy and Washington as the impetus for Nurse Ratched to send McMurphy, Chief, and Charlie Cheswick (who doesn't commit suicide in the film) to the Disturbed Ward. Perhaps the most telling difference between the film and the novel is the ending.