In short, people knew about plagues before they arrived. News of great illness and death will spread, whatever the technology available. Lords would send riders to inform their allies; traders would share reports of being turned away by quarantines; clergy would learn of mass burials. Our ancestors felt the same sense of impending helplessness as we do.
Also inaccurate is the notion that simply suffering through the pandemic would more rapidly return us to normalcy. The economic effects of the 1918 flu pandemic were dire, but research from MIT suggests places with stronger public health responses — shutdowns that started sooner and lasted longer — had better economic recoveries. In the Twin Cities, where I live, Minneapolis ordered closures three weeks before Saint Paul and came away with both a lower mortality rate (388 deaths per 100,000 vs. 481) and a stronger economy (30 percent employment gains between 1914 and 1919 vs. 15 percent). The economic analogy between that pandemic and ours can only go so far, but this history at least casts real doubt on the economic preferability of ignorantly letting the disease run wild.