The answer to the first question is: quite possibly, but with something like tuberculosis instead of the plague. Less immediately scary, but more harmful: resistant forms of more common bacteria will create serious risks when undergoing any sort of surgical procedure. We could get back to the days when your biggest risk of surgery was dying from infection afterward.
The answer to you second question is: no, we haven't really been working on it. But the big problem is that we can't just invent new classes of antibiotics overnight. If one of these strains takes off, things will get a lot worse before they get better.