There’s no evidence whatsoever to support that. Even if antibody titers were to decrease, the real question is whether Memory B-cell lymphocytes remain to ramp back up that response to an exposure. That’s how antibodies work: your body doesn’t sit there producing antibodies 24/7 to every single pathogen you’ve ever been exposed to. That requires an absolutely massive amount of energy. B-cell lymphocytes produce antibodies for a limited period of time and then 90% die off, leaving 10% dormant as Memory B-cells.
Same for those previously infected as it is for those vaccinated. It’s the same immune response because whether the dendritic cells encounter SARS-CoV-2 S proteins presented due to vaccinated or the dendritic cells encounter SARS-CoV-2 S proteins on the surface of SARS-CoV-2 virions, they’re still just taking those antigens back to the lymph nodes to begin T-cell lymphocyte production.
So then natural immunity is fine as well as those vaccinated not needing booster shots.