It has been my experience observing friends and relatives that often there is a remarkable precision to the prediction--especially with metastatic disease, cancer.
Holding out false hopes based on wishful thinking and a do anything to prolong life attitude, no matter what, no matter how expensive, no matter how iffy, no matter what the odds, does not seem to me to be prudent or wise, and certainly isn't careful use of our dollars.
Eighteen months ago my brother in-law died. He had been told he would die around christmas, and he in fact died on new years day, a few moments after midnight. For 4 years ahead of his departure, it was quite predictable that his demise was going to occur at about that date, no matter how much money (chemotherapy) would be thrown at his disease. A person reaches a point at which there is certainty within time bands that the end is going to happen.
There is a big difference between withholding care that provides comfort, something that is not in any way moral, and putting oneself through agony in a hopeless quest for a few more hours or days.
Yes, we hear of "miracles" from time to time, but in the real world there is both an inevitability of an end, and a predicatbility that a disease will run its usual course.