There is a big problem with optimistically assuming immune systems will respond like SARS even, because we know in general terms the more severe the symptoms the longer the immunity lasts, but wait ... huge huge numbers of people with Covid-19 are asymptotic, that is not the cases with it’s SARS and MERS relatives! wake up people, herd immunity is delusional and dangerous. more likely is very short immunity, just like the other 4 Corona family virus which cause many of our common colds, high asymptotic rates, and reinfect us very very frequently and NOT due to mutations!

http://www.columbia.edu/~jls106/galanti_shaman_ms_supp.pdf

If those SARS numbers are in the same vein as what is true for COVID19, the only answer is a vaccine. Otherwise our current state of affairs is the new normal for the foreseeable future.

It's estimated that ~14% of common cold cases are caused by coronaviruses (HCoV-OC43, HCoV-229E, HCoV-NL63)... so although it seems particularly difficult, if we do manage to discover how to develop effective vaccines against Covid19, perhaps the silver lining is that vaccines against the related viruses responsible for a significant fraction of the common cold will be in reach.

https://en.wikipedia.org/wiki/Human_coronavirus_OC43

I would also argue vaccine is not likely for many related reasons.

In that case COVID19 will play out like the 1918 flu, it will hit in waves that only mass quarantine will help mitigate, until enough immunity is reached. Likely 18 months - 2 years.