If death rates return to "normal"

 Normal in this case means the greater human history that does not include that tiny fraction that is the 200 to 300 time span known as the modern era.

In reading The Field and the Forge, Population, Production, and Power in the Pre-Industrial West, John Landers sets the table by describing expected life expectancies during the time period as compared to now.

The century after 1870 saw unprecedented changes  in the mortality as well as fertility of western populations. The average expectation of life at birth, which had rarely been much above forty years and often was much less, almost doubled, and the structure of mortality rates by age and cause of death was transformed. Previously some 20 to 30 per cent of live-born babies in most populations had died before their first birthday, and the proportion surviving to age 15 was rarely outside the range of 35 to 50 percent.  By the 1970s mortality risks had all but disappeared from infancy and childhood, and younger adult levels had declined dramatically...

Pre-transitional mortality regimes were all dominated by early death from infectious disease but they were far from uniform in other respects. Overall mortality levels fluctuated considerably,  in both the long and short term, and there was a great deal of spatial variation.  English life expectancy stood at a little over forty years on the eve of the transition, having apparently fluctuated between the ages of roughly thirty and forty over the preceding three centuries...English communities on the whole enjoyed mortality advantages over their early modern continental neighbours, most of whose life expectancies are likely to ranged from the high twenties to the mid-thirties [notations deleted, page 28].

He goes on to notes that the peaks and troughs in the demographic cycle (in simple terms the Malthusian boom and bust cycle) of as much as 20 to 30 percent.  Severe disease episodes, such as the Black Death would cause very sudden severe drops: as much as fifty percent being likely.