Real actuary speaking here. Societies generally put resources into producing things that the society wants. They put more resources into things that they want more of *relative to other things that they don't want as badly*. It is that relative allocation that is important. If we didn't want to live longer lives, we would spend our resources on present day consumption rather than on medical services. The fact that the cost of health care keeps going up and up is merely a reflection of the fact that (in the 1st world) we have (more than) enough food, adequate shelter, and plenty of shiny things to keep us happy, so what we really want to spend money on is a pill that keeps our bodies younger for longer. So unless we "unlearn" all the things that give us this phenomenal productivity (through natural catastrophe, war, plague, etc.), we don't have to worry about decline.
One lecturer put it well by saying that he couldn't wait until we are spending 99% of GDP on health care, because at that point all of our wants and needs for food, shelter, entertainment, intellectual challenge, etc will be satisfied for pocket change so the only thing actually worth putting society's resources into is extending life.