>>95923172 (OP)
They get arrested for murder and crimes against the intelligent peoples of the world, probably put to death. That is, of course, assuming they aren't gunned down in self-defense by said Lowborn (the closest thing my setting/system has to tieflings) since it's modern fantasy and automatic armor-piercing firearms and explosives exist alongside magic including the powers martials have to buff themselves to superhuman levels.
A Roman Legion would get absolutely annihilated in my setting as a result.