The sad reality of living wills and DNR orders is that they can be over ridden by your next of kin the minute you become incapable of making your own decisions. I've seen it happen many times.
I belive it is a persons right to decide the quality vs quantity issue. And the laws should be changed to prevent families from reversing decisions patients have already made.
My personal view:
I have cancer. It is incurable. It's slow growing, but the 5 year survival is 50%. 10 year is about 10%. It's metastatic carcinoid. Although it generally starts by the appendix, it has a real affinity for the liver (80%) and the heart (40%). So far, other than recovery time after surgery, it's had very little impact on my quality of life. I still work full time. I still Jeep. I still SCUBA. I still train 60-90 minutes a day at home and 2-3 hours 3 x week at the dojang. But when my quality of life reaches a certain point, I'll have a nice party, tell my family and friends that I love them, and check out.