Simply put if there is no effective vaccine or definitive medication this virus will permeate the population. People who survive this, as in the days of bubonic plague, will have either the genetic capability of not getting infected or the genetic capability if becoming infected but not critically ill or dead. Those that have the genetic susceptibility to the virus and do not have the genetic capability to recover will die off. When this virus circulates enough times those with the genetic susceptibility for severe and infection or those with the genetic susceptibility for infection and associated co- morbid environmental factors will die off and the susceptibility gene will be weeded out of the population. That is true “herd immunity” The problem is there will be a lot of suffering and deadly culling before such “herd immunity” is achieved.
...and if there is only transient antibody production there will never be and herd immunity at all.