“My guess is that by June or July of 2021 people will be acting pretty much as they did in June of 2019.”
I would agree. The vaccinations will be done by then, so the biggest danger is over, and the health authorities might simply decide to let Darwinism run its course and the anti-vaxxers can take their chances. Also, 'flu is always less of a problem in the summer, so it will probably be on a downward curve by then. I am hoping that it will not be a repeat of the Spanish 'flu, which lasted well over two years and got worse over time, but I think we could tame this one in the spring.
One issue with herd immunity is that there seems to be massive underreporting of COVID cases. A number of acquaintances have had it, but very few of them reported it. They were lucky and got the milder version with no complications.
Another issue is that COVID is becoming highly damaging to the economy, and at some point people will say that the cost outweighs the health risk and we have to get back to some sort of norrmality, albeit with some precautions. But in the last resort COVID is not Ebola. It remains to be seen whether it will mutate to a milder version and maybe become a seasonal nuisance.