Who gets to decide when we die?

I 'do' a lot of bioethics.  I read lots of ethics cases, research studies and journal articles. I talk to and share resources with others, from around the country, who are doing ethics.  I am the chair of our pediatric ethics committee at the hospital.  I am involved in several discussion forums and listservs that focus on bioethics.  I do ethics consults at the hospital.  And, I am currently taking the first ever pediatric ethics certificate course - a year long course that has rigorous requirements to enable one to receive a certificate in bioethics at the end.  Throughout all of these activities, I learn so much.  The topics are sometimes fascinating, and I always educational.

Yes,  medical boethicists are, often, very deep thinkers.

And, I have a confession to make, and I'll make it to you all tonight!  Although I am considered to be "one of them" (medical ethicist) by training and profession, I am not the deep thinker, philosopher type that characterizes some of my colleagues.  They are philosophers who can talk/argue/philosophize about a topic for hours.  I am simply one who lives in the middle of ethical dilemmas.  And sometimes they are messy.

So, I am perplexed by a recent ethics online discussion and would like to ask you all to weigh in.  The discussion goes something like this.

Dr. X is caring for Mr. Y, a patient in the hospital.  Mr. Y's daughter, Miss Y, is his surrogate decision maker.  Mr. Y has begun to decline rapidly and Dr. X has asked Miss Y if she wants to make him DNR (Do Not Resuscitate) status.  Miss Y states no, she wants her father to be a 'full code', receiving CPR and all other supports to help him live.

Later that day, Dr. X determines that Mr. Y is 'too sick' to have full code status, and reinstates the DNR order.  Over the course of the next several hours, Mr. Y continues to decline.   Mr. Y dies, with no attempt to resuscitate him, despite the fact that Mr. Y had requested to be have full code status (all resuscitative care takes place).  Dr. X states that he was very busy and therefore unable to contact Miss Y about changing his code status back to a DNR.  Dr. X states that Mr. Y was so ill that there was no reason to try to resuscitate him.

So, my question(s):
Who gets to decide?  Does a doctor have the right to determine when - and if - a patient should receive life sustaining treatment?  Or, is that decision the patient's/surrogate's decision to make?  Is this a matter of poor communication on the doctor's part?  Was it unethical for the doctor to make decisions that were different than the patients?  Or, does the doctor have the right to determine when he feels the patient's/surrogate's assessment may be inappropriate?  This patient was apparently dying... would you feel differently about the doctor's actions if, for example, the patient was just moderately ill?  Or, if it were you or your family member?

Ethics is never easy.  Some go so far as to say it is dirty business.  I am looking forward to hearing your thoughts!