I have an idea on how to mitigate this kind of attack in future. It would be somewhat complex to implement however. It would be possible to hide the real ips of the servers from outside though the use of reverse proxy and multiple login servers. in the event of attack it would just be a matter of changing the login servers ips (easy to do as they would be lightweight proxies, rather than whole game servers, and would be easy to spin up in the cloud) It would be quite an effort to implement however....and probably not worth it given the rarity of this kind of event.