Where is this damage...?
Right around the fin box?
If so, it should not be a problem with water intrusion as the fin box insert extends more that 1/2" in all directions around the fin cavity.
If it's on the deck, and you only see the brown foam layer, is the glass on that brown layer cracked?
There is at least one additional layer of glass under the brown high density foam, so a little touch up paint and your board should be fine.