The usual form of the plague, carried by insect vectors, is rarely fatal and easily treated (bubonic plague). However, when arasolized (pneumonic plague) it is almost uniformly fatal, even with modern ICU and antibiotic therapies. On any given day in our city, hospital beds are at a premium, ICU beds even more so. Just 100 people in a city needing an ICU bed all at once would swamp the system. Now imagine a few thousand needing an ICU bed. I’m sorry, in an attack like this one almost everyone infected would die, modern medicine or no.
Yes, the pneumonic form would be much worse, but if infected flea infested rats are introduced to a densely populated slum, for example, the results would not quite significant. If victims are not given the correct ABs very quickly, they will die.