Herd immunity is always achievable, especially if 'everyone' is going to get it.
It then depends on the variants and the antigenic drift' of the virus. Flu there are four strains and they're changing all the time, hence having to 'live' with it.
Maybe 'the herd' can tread down on this virus to a greater degree. If we are going to decide to stop hiding from it, (as implied) that carries risk BUT may also carry a benefit as the number of infected increases rapidly(ie the herd)and fresh hosts decline . The virus then has to be clever enough to mutate enough to either increase severity of symptoms (enough to cause concern) or avoid existing immunity (natural or vaccine) altogether, basically putting us back to square one.
It's just as likely to not be smart enough, and we end up so many steps ahead that it fades out. Sars 1 etc.