Elders embody society. Culture is transmitted by grandparents. I learned to read on Grandma’s knee because she had the time for it while Mom worked. Kill-off elders and society is decapitated.
Quantify “productive years”.
More than a few old farts MrsRico and I associate with work productively. And retired old farts with medical training are being recruited to help with the crisis so someone thinks they’re vital. If we kill off everyone over age 65, removing all their experience and skills, how long would the rest of the nation last?
Back to the OP - and no more jokes about how it’d be nice if humans were civilized i.e. decent. “Civilization” is literally urban life; “civilized society” is a network of housing clusters plus support facilities e.g. food and energy production. Recurrent pandemics are The New Normal for our globalized civilization. I expect rigid authoritarian controls and ubiquitous surveillance. Forget any dreams of “privacy” and “freedom”.