If he had filed this five seconds before he quit, it would have been posted in the normal manner.
I do not see a problem with it being filed after he quit, since the purpose of a Magistrates case of this nature is not to fix the situation for Menethil, but to make a final determination as to whether what you have done was against the spirit of the Social Contract, and if so, deliver a punishment deemed appropriate to deter you from doing such things in the future.
Don't give me BS about your rights as a player when you felt absolutely no compunction about trampling all over Jason's rights just because he happened to be playing the rule of a realm that your character's realm was at war with.