Interesting, when I search for the economic consequences of the 1918 Spanish flu, I do not sem to find a depression, but a decade of very high economic activity in the 1920s.....WHat happened there??
I believe what happened may be similar to what happened after the Plague during the Middle Ages. It is a grim thing to think about, however, the repercussions of mass deaths results in three impacts to the survivors:
One, there are fewer workers left so most people who want a job are employed.
Two, employers have a significant shortage of workers available to hire, and therefore wages are increased to compete for talent. (You might think that there would be less demand for consumer goods, and this is true; however, you still need the same number of people to maintain the infrastructure (roads, bridges, electric grids) as well as a required baseline of employees for a company regardless of demand.)
Three, during the Plague, those who survived were the inheritors of the estates of family members who passed away.
Like I said, this is grim stuff, however if you want to read more here’s an excerpt from a history after the Middle Ages Plague.
There were two kinds of people who especially benefited from the squabbles brought about by the Black Death and the endless litigation that was the result. The first were the "common lawyers" (so-called to distinguish them from civil - Roman - lawyers who practiced in ecclesiastical courts).
The common lawyers were graduates of the Inns of Court, the four residential law schools cum bar associations located in Westminster in London (they are still there today). They made their money protecting, expanding, and defending the gentry estates. There was actually a shortage of them, and their fees were high, but no gentry family could endure long without their services. Since medieval English procedure did not allow a defendant to be represented by an attorney in a criminal trial, the criminal justice bar was almost nonexistent.
Many of these barristers specializing in property and inheritance cases were on permanent retainer to leading families. It was not enough to know the law - not an easy thing to do because property law was frequently changed by judicial decisions as well as by occasional legislation (as in the United States today). They also had to be expert at drawing complicated documents in a highly specialized language, law French, and it also helped to know Latin and English, which were also used in the law courts. Above all they had to be expert "pleaders" (later called barristers), attorneys who were licensed to appear in court, stand on their feet, and with little or no aide-memoir argue immensely complicated cases before judges and juries for hours or days on end.
The other beneficiaries of the plague, besides the lawyers, were women of the gentry class. The common law had a procedure for protecting widows, partly because the gentry landlords engaged in serial marriages with wives who died like flies in childbirth and were often gone by age thirty.
The heir to the family estate was usually a product of the first marriage and the widow, wife number two or three, was his stepmother, sometimes younger than the heir. Oedipal tensions ("that sexy young wench, my father's third wife and now his widow, is eating up the old man's estate," a great plot line that Shakespeare and Hollywood missed) could inflame an heir's greedy disdain for taking care of his stepmother or even his actual birth-mother, in this cruel, selfish society.
Therefore, the law stepped in and decreed that every widow had a right to "dower," one-third of the income (not the capital) of her husband's estate until she died. Within forty days of her husband's demise she was supposed to vacate the family mansion. But one-third the income from the family lands would allow her to live comfortably elsewhere and play the role of the grand dowager. (source)