Quality of life

Judaism believes that life is sacred no matter what the quality of life is. I have never thought that much about this until now. My father who is quite elderly, is in the hospital on a ventilator. When he first had breathing problems the people in the hospital asked about a DNR and talked about quality of life etc. I am really torn about this. I can see both sides. On one side is the argument that what value is there in life on a ventilator where you may be living but you can't communicate or do anything. Their is a financial aspect as well. Society has limited resources and spending hundreds of thousands to milions of dollars to keep an elderly man barely alive may not be the best use of resources. On the other side is the idea that every second of life is precious and we need to preserve it no matter what and who are we to decide what is quality of life. 

Truthfully, I believe that the Jewish position was founded in a completely different time and needs to be updated. In the time of Chazal, these issues basically did not exist. People either lived or died, no one lived with chronic illness and certainly no one lived for years in a a non-responsive state. In the time of Chazal my father would have been long dead. Chazal never imagined a state where we could keep someone alive for years with something like a ventilator. we have a similar problem with brain death. It is clear that Chazal did not understand the human body and therefore their discussions of death should be irrelevant. Of course halacha doesn't work that way and everyone tries to reinterpret various statements to support their position.