i am all for the prospect of guards, but i do think their should be NPC guards that patrol at the final stages. you know, something like check if the "scout" of a guard is within distance to hear the sound of the brawl, and have them respond to /shouts with a few words in them, like "Help!" or "Guards!" then their should be a server roll to decide if the guard is professional or a first day recruit type person as to whether they decide to call for back up or go it alone. there should always be a chance that the assailant gets away with it, as no crime prevention system is perfect. though i do think the system should never be fully automated, as that would take away from the RP feeling. maybe we could have a trial system set up. something simple, where people can volunteer for jury duty, and if their are enough of these jury marked players. the case is actually played out. defendant and complainant present to jurors, jurors vote guilty or innocent, or even fivorius if they think the complainant should be the one getting time.
of corse if the player desides to attack the guard, it should be just like any other NPC fight, being that the player could die. but also, if another patrol man comes across, it causes all the guards to attack this person on sight until they are killed.