The defeat of the king-men meant the reestablishment of the rule of law. Therefore, Mormon makes sure to note that those captured king-men received their trial, according to the law. They were executed, but also according to the law.
The thirtieth year ended with this particular crisis having been contained. There were still Lamanites to worry about in the eastern borders, but the internal division had been resolved. The armies in the field would now be able to receive reinforcements and provisions needed to defend the lands already retaken, and to begin the task of retaking the rest.