Natural immunity lasts far longer than 6 months. That claim is propaganda designed to get people to accept constant jabbing. The antibodies that are produced during an infection wane, but the immunity is not dependent on those antibodies staying around forever. Your immune system keeps a memory of how to produce those antibodies and will produce them again when you are reinfected.

Just like you get a lifetime immunity to chicken pox you get a lifetime immunity to covid. And no, the rare exception of people getting chicken pox again does not disprove this. Exceptions exist to everything but do not disprove the rule.

If there is a significant mutation to covid then obviously nothing can stop that. However, natural immunity will provide protection against some mutations while the vaccines can not.