That's a serious damage. We had 35-47 knots mean wind yesterday, so I saw some broken boards here too.
Anyway, on your board, not only the top fiber layber but the sandwich and probably the fiber under the sandwhich is broken too. It will not hold up if you only patch it up on top like you are suggesting. You need to route/sand the sandwhich and possibly even soome of the EPS. Then build it up from the bottom up with eps (or expanding PU) then fiber, carefully connecting it to the original layer, then sandwhich foam, preferably vacuumed and feathered in with th original, and finally fiber on top, I would go for three layers 100g, first on 40cm then on 25cm and then om 15cm wide. Before putting on the top layber, you can also put in some 10-15cm long and 2cm deep wood reinforcements across there the break was, but with a good ground work that should not be necessary.
So it is some work to do this. But fully possible. And its better to do it thoroughly from the start.
Even though your board is not in two pieces, I think the best illustration of what you have to do is this one: http://www.boardlady.com/snap.htm