If necessary, there will be adjusted vaccines to improve duration and address variants.
Worst case might be an annual booster, like the flu shot but I tend to think that once the variant production slows down that boosters won't be required as often.
Also it depends on whether the goal is to avoid death, or avoid infection? At some point we'll probably be good as long as people aren't afraid of dying... good chance that immunity of any sort will provide fairly long protection against severe covid. Just like the flu shot... if you're at risk, better get the booster. If not, it's a personal decision based on the nuisance factor.