Like all cells, antibodies die off after a period of time. A human body may (or not) be able to efficiently replace or replicate these antibodies. Whether the original antibodies were generated naturally (by sickness) or artificially (by immunization), an essential question might be, What is the lifespan of antibodies specific to SARS-CoV-2?
It is likely that because of the novelty of SAR-CoV-2, the medical community has not yet had sufficient time to study this question, however past studies on Coronavirus types should be available.
(for example MERS antibody studied MERS antibody longevity. I don't know if that provides any clues regarding SARS-CoV-2. I look to members at this site for guidance)