Nah, you would be correct for 99% of the time. Grabbing the GUID of all players that were online when the king first came under attack WOULD punish players that logged out instead of protecting the king. But it would suck if you had to go to work, or deal with some other real life responsibility, so you log out, then you get punished.
I only want to catch the players that used to log into their secondary character while the king is under attack, then re-logged back onto their main character once it dies.
Thanks for your suggestion though! I'm always glad to receive help