Abinadi is pronouncing this curse upon those who are present. Mormon does not list who they are, but it appears to be more than the priests and King Noah. While the priests do suffer during their flight through the wilderness, they eventually join with the Lamanites. Thus, their ultimate fate does not seem to fulfill this prophecy. Rather, in this public setting, Abinadi is speaking to those who will become the people of Limhi. They certainly suffered from bondage to the Lamanites, and fleeing from their homes to Zarahemla would fulfill the prophecy of the scattering.
In the ancient world (and until relatively recently), executions were typically public. In Mesoamerica, human sacrifice was publicly performed. The social reasons for public execution include the emphasis on the social sanction against the person and public disapproval of his crime. The punishment stands as a clear and present warning to all who might have sympathized with the one being executed. In this case, Abinadi was seen as a threat and therefore was publicly executed to demonstrate the fate of those who oppose the king.