Core is not going to rot in the absence of water. So, if it's in good condition now and simple steps are taken to prevent water intrusion, then you're fine. IT IS NOT A BIG DEAL, though it will make the boat lighter, faster and stiffer.
Coring is a larger issue in decks due to the many fastener holes and the often careless installation of hardware.
My boat is a 1981 hull and the core is as good as the day it was installed.
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