This is factually incorrect. Even if antibiotics become less effective (they are not becoming ineffective, is just that resistant bacteria require higher doses,

This is factually incorrect. Even if antibiotics become less effective (they are not becoming ineffective, is just that resistant bacteria require higher doses, which start to become problematic from the side effects point of view). First of all, we will still have the Germ theory of Disease. Much of the early gains in lifespan from modern medicine came from the awareness of the correlation between cleanness and healthiness. For as long as we can support infrastructure for proper sanitation and disposal of dangerous agents, those gains will persist. Second, we will still have vaccination. Many dangerous diseases are kept at bay not by heavy use of drugs but by immunization the population instead. This technique is also subject to diminishing returns due to bacteria evolution, but the dynamics are different. Over use antibiotics and you end up with resistant diseases; reach full immunization and you root out the disease out of your population. Third, we have better palliative care now. Even if everything else fails, we are better prepared now to keep people alive long enough for their own antibodies to fight off most diseases. This will be shitty for our current expectations - to be able to take a pill and bounce back in a day or two. But it does not mean either that half of our children are going to die of colds or tummy aches or anything like that.