Does consumption decrease directly lead to a shift in Aggregate Demand curve to the left?
You mention here a crucial point that falls nowadays more and more in oblivion, that is the well-known aggregation issue across consumers. The described behavior of the individual and aggregate demand curve can only be expected to be observed when the essential properties of the individual demand functions can be bequeathed to the aggregated demand function. For this case one needs a particular type of utility function, it must be of Gorman form, that is, the utility functions of consumers must be quasi-linear, or to put it differently, they must be linear in the numeraire good to get an aggregate demand function that inherits their properties from the individual demand functions (cf. Varian Microeconomic Analysis 1992, third edition, pp.152-154).