From that map, it looks like 5 towns got razed. Assuming an average population of 2500 per Town (It's a value I'm acquiring from Google Medieval town population so YMMV), then that means a total population of around 12,500. This of course assumes all 5 settlements were towns and not Villages, which have a smaller population. I would give an upper estimate of perhaps 2,500 dying and 10k making it out, but it's possibly lower.
The majority still survived, which is a far better scenario than the alternative.
I still think you are being a bit optimistic. There are also villages too small to be on the map to consider and probably a lot more of them. Someone has to grow the food for all those coastal cities.