Antibodies don’t remain forever for any infection. The B-cells that produce them die off shortly after infection subsides to avoid wasting energy. What remains are Memory B-cells, which can kick off the antibody production again very quickly should that pathogen be encountered again in the future.
If your body’s B-cells and T-cells were constantly being produced and running at full steam for every pathogen you’ve ever encountered, you’d die from exhaustion pretty quickly. The loss of antibodies isn’t that concerning so long as T-cell and B-cell response remains available. Time will tell if that’s the case. It would unethical to test that by purposely reinfecting someone who’s had it before. So far I’ve seen no credible reports of actual reinfection. The early reports were due to anomalies in the PCR testing due to viral proteins remaining present in subjects longer than expected.
That was my understanding - that the body should remember how to produce the antibodies but I keep reading breathless reports about reinfection and lack of immunity that I was beginning to question my layman’s knowledge.
There’s also some speculation that the virus goes dormant for awhile and then comes back which is why the tests are “clear” - but I still think that comes back down to test failures.