My footbeds are more than fifteen years old, and I've yet to have a better pair made (I've had several others built since, but none have worked as well for me.) They are the molded-cork-type footbeds--I don't think other types tend to last as long.
But feet DO change over time. Some top bootfitters recommend new footbeds every couple years.
You might want to post your question in the Gear section, and see if Jeff Bergeron or one of our other boot gurus will share their experience regarding footbed longevity, and the need to replace them to accommodate changing feet.