Retesting positives won't work because we don't know whether it's independent. If there's some rare common cold coronavirus antibodies that some of the population has, that set off the test, they'll still have them later.
Not sure how well having the Bay Area do one thing, and large chunks of the rest of the country dash to herd immunity is going to work.
A little, but not anything close to what we consider normalcy. And you get to maintain them forever, or until a vaccine arrives.
Of course, our case count is so high right now. If you get Rt down to a miraculous 0.5, it's like 180 days before you can get to the point where contact tracing is effective. And you probably don't achieve an Rt of 0.5.
Not sure how well having the Bay Area do one thing, and large chunks of the rest of the country dash to herd immunity is going to work.