Good question, but then you already know the answer. As long as we can, we will. Should does not enter into it. But thanks for a very scary look into a possible future. SHould I be placed in that position, I will just go home to die among friends and family. I would not want to live like your example.
When you factor in the money, it is a whole nother egg. Should still does not enter into it, but the ability to pay does. I am not saying Should Should not enter into it, I am saying no one is going to make that call (other than the patient). And sometimes, that 70 year old (or 59 year old) is doing exactly what you want. Remember Barney Clarke? before trying an experimental procedure on someone who has perhaps many years to live, others, with absolutely no hope, can be used - with their permission. Again, the cost of Barney's procedure was outrageous, but it helped to figure out if Artificial hearts were viable.
But you have again introduced another factor into the should arguement. Yes, in that situation, you have to make judgement calls based upon limited time. IN the case that BlueDev described, that was not a factor. I do remember the MASH episode where Blake asked pierce to consult with him over a case that would not make it. But then the decision is not "should" in that case, but how many are saveable, and how many are too far gone. The question changes then.
That is why you make the big bucks (or at least he does). I do understand, but I would never want to make that call. I can empathize with both the resident and the attending in that case. You are right, sometimes, doing nothing is best. But it is also the hardest thing to do.
Time is a resource. and one that is hardest to augment.