If there is no significant herd immunity due to mutations or whatever, then really, I don't see how any lockdowns will do more than simply limit the numbers of sick over any given period. You can lock everyone down everywhere in the country for a year, and at some point there will be a new patient zero that has been carrying some mutation of the virus, or someone coming in from abroad (including illegally) and an encounter with some very susceptible person, and we start all over again.
Also if we create no vaccines that do any better than the current runs of flu vaccines, then it seems we continue to be in the same boat. This may be here to stay, same as the common cold, except with more serious consequences for the at-risk population. To be a little science-fictiony or Darwinist, this may be a global event that kills off certain gene pools.