The Order of the Avenging Star by Will Conway

When the Order of the Avenging Star is brought down in a devastating assault by its longtime enemies, Gavner, Donato, and Darselz suddenly find themselves in a world newly hostile to them. In order to ensure the survival of the human race, they must navigate a continent covered by their enemies, all while surviving the ghosts of the Order's past - but will they learn from the mistakes of their forebears, or doom humanity to extinction?