Considering in the developing world babies are not dying of infections, its safe to assume that it can last a long time.

How does a lower infant mortality rate indicate lower antibiotic misuse? Antibiotic misuse could be constant as a % of overall antibiotic use.

A lot of negativity in this thread is probably because they're saving the "wrong kind" of infants

Well, yet. Resistances are on the rise. It will probably get a lot worse before we start using antibiotics more responsibly.

That is not how it work. Resistant strains, once evolved, do not need to 'start from scratch'.

It's much more complicated than you seem to think, otherwise there would be almost no non-resistant strains left.

For example, there typically seems to be a cost associated with maintaining resistance, and particularly maintaining multiple forms of resistance, and strains will often drop resistance absent constant selection pressure.

Adding onto this, I saw a very interesting seminar a few years ago from a biologist who sequenced bacterial samples from the arctic permafrost. He found resistance genes for antibiotics that had definitely not been created by humans at the time that the samples were deposited.

So "new" antibiotics aren't actually new, and resistance to them probably already exists somewhere -- bacteria have been fighting this war for as long as there have been bacteria.