We have eradicated one human virus in all of history, and it took a highly effective vaccine and a hundred years. The long tail is very long.
That immunity will likely be durable for many years (based on the somewhat recent study of HCoV-229E).
That will force the virus to mutate to achieve true escape immunity (a strain, not a variant, which can reinfect everyone all over) which will likely come at a cost to fitness, since one or two mutations to spike isn't enough, and there will need to be a few tens of mutations to spike.
That virus strain will not be as transmissible or virulent as what we are dealing with now, because it has had to make those costly "decisions".
And this is important for people who for medical reasons cannot be vaccinate or who are at high risk even if they are vaccinated. They're much better off being infected by subsequent strains down the road than being infected with version 1.x of this virus.
This is also what has been observed in the past with 1918 H1N1 which later evolved into seasonal influenza.
I’m not convinced you can absolutely guarantee these changes will make the virus less dangerous, we could be unlucky and it could become worse.
The sum total of mutations necessary to achieve immune escape and overcome herd immunity is a lot more likely to come at a cost to overall fitness.
Also I can't guarantee that West Ham United won't win the Premier League, but the safe money is all on Man City.
Paper on the possibility of mild disease endemicity:
https://science.sciencemag.org/content/371/6530/741
AP coverage of that paper:
https://apnews.com/article/common-cold-india-coronavirus-pan...
From what I can tell, almost all public discussion of the future of Covid is similar to a "happy path."
Covid is endemic. It is not going away. It doesn’t meet any of the standards set up by the WHO for eradication, and even if it did, it would take decades of intensive work, on par with what we’ve been doing for polio.
https://www.gatesnotes.com/health/in-pakistan-victory-agains...
Polio and Measles are doable, and at this point more logistical and political problems than biological ones.
It isn’t a trivial problem. And oh yeah: Covid is in those countries now, too.