In North America (specifically, one site in North America, the Hell Creek Formation in South Dakota), which was obviously fairly close to the impact site (considering its size), huge wildfires, as just one proximate killer resulting from an ultimate extraterrestrial cause (and also implicated in supervolcanism), should have wiped out most everything. Yet amphibians, mammals, bony fish, turtles, champsosaurs and crocodilians all survived, while sharks and other elasmobranchs, marsupials, lizards and dinosaurs died out or suffered very heavy losses. This pattern doesn’t fit the “global wildfire” scenario. Nor does it fit the “acid rain” or “nuclear winter” scenarios. Indeed, the ultimate cause which most neatly fits the survival pattern in this region is neither supervolcanism nor asteroid impact; rather, it is seaway regression.
While the Chicxulub impact was certainly no picnic, we simply lack sufficient evidence to claim with any certainty that it was responsible for the whole, or even the majority, of the numerous extinctions at the end of the Cretaceous. Everyone likes to focus on dinosaurs, but there were several groups that died out completely, and others that suffered significant losses, while yet others breezed through.
The impact may have combined with, or possibly even initiated, the massive volcanic plumes which were also occurring at around the same time. But we lack sufficient resolution in the fossil record to be able to identify a timetable of extinctions, in order to determine if they happened quickly (on the order of a few hundred years, perhaps, if impact were the primary cause), or were more prolonged (over a few millenia, perhaps, if volcanism was primarily responsible for most of the deaths, or likely even longer for seaway regression).
So, a Chicxulub-sized impact would be tremendously devastating, but would also obviously be survivable. The problem is, we don’t know what the “trick” to survival really is at this time. So we also can’t really say whether humans would be among those lucky enough to survive the next such impact.