Brainstorming some possibilities, not taking myself too seriously:
--2020 will be remembered as a year of death and disruption; the economy will suffer massively, perhaps enough to count as a recession.
--Many old people will die (something like 10%?) this is a big higher than the current fatality rates but I predict they will rise once hospital systems are overwhelmed. This will have a few knock-on effects: 1. Health care expenditures will drop for the next few years, since old and sick people are the biggest source of such expenditures and the population of old and sick people will be substantially smaller. 2. There will be a noticeable increase in average spending money available to younger people due to inheritances. 3. Politics in the USA at least will shift noticeably (though not dramatically) to the left, since the dead people will be disproportionately right-leaning. 4. Politics worldwide will generally shift in a more radical direction, since the proportion of young people to old people will increase. 5. One of the contenders for the US presidency might die before the election. (This is unlikely even if 50% of the world gets infected, but it is likely enough to deserve mention I think.)
--China's dramatic and draconian measures to contain the virus will come to be seen as a success story, something that would have worked if only other nations had behaved similarly (and perhaps, if China keeps its border closed, it actually will work for China at least?). This leads to an increase in authoritarianism in general around the world, made substantially stronger by the general tendency of authoritarianism to rise during crises.
--The world will, in general, take pandemic risks much more seriously from now on, making it substantially harder for something like this (or worse) to happen again.
The world is probably going to lose
52.5-10% of its population (380190-760 million, see here for the reason for my edit), worse than the Spanish flu even on a percentage basis. I didn't realize this until now (or rather, these facts didn't become salient until now), but the current CFR estimates for COVID-19 are based on hospitals not being overwhelmed, whereas Spanish flu CFR was based on hospitals being overwhelmed (plus they didn't have the life-saving technology we have today anyway, like oxygen concentrator and mechanical ventilator). If hospitals are overwhelmed, which seems very likely at this point, most of the people needing to be hospitalized (10-20% of infected, which will themselves be ~50% of world population according to epidemiologists) will probably die. See Forget about mortality rate, this is why you should be worried about coronavirus for more details but I actually arrived at this conclusion myself shortly before coming across that. My own realization was triggered by reading this post.Update on Diamond Princess: as of now, Wikipedia says that the death toll is 14, or 2% of the passengers who tested positive within the first month. However, the dead all seem to have been elderly (there were many elderly passengers, as expected for a cruise liner). More specifically, 11 of them were over 70, another was over 60, and two others were of undisclosed age due to family wishes.
I don't know how to adjust those results for demographics, and of course you can't use them to predict what would happen without hospital care. But it's a ... (read more)