If you have a core shot then you should get that hole filled before cancer hits. Ignore the people who say it isn't a big deal, they are ignorant and passing along bad info that could lead to the end of your investment.
Sure you could get lucky and no water will ever penetrate your core. A more likely scenario is that water will work it's way into the exposed core or into gaps between the now damaged ptex and core. Since we snowboard on snow and snow is colder than water the chances of the water expanding due to lowering temperature is high. That expansion of water will tear your board slowly apart. This isn't rocket science, it's really more basic engineering.