Umm ok the key word in this case is EMERGENCY, meaning it was not planned nor intentional, it just happened so the only way you would have had any warning was if cryptic staff were time travellers or able to see into the future.
I agree with the others, an ingame message a few minutes beforehand, say 15 min so we know, with an update every minute would be quite handy.
Also, when logged out and trying to relog, due to not knowing what caused the disconnection, an
error message that the servers are down is imo probably more helpful than returning the error that
username/password are incorrect (even though they were correct)