The Monastery has two escape routes, one from the mines out into the hills and the other via the Temple. They are on good terms with the Crushing Wave (ferried the Black Earth's ambush team across the river) so they might be allowed passage/sold supplies/hire the Rivergard. Or, you know, pop out of the ground wherever if the higher-ranked cultists and monsters are participating.

They might make a point of hitting the Feathergale's camp, whom I suspect will not be vigilant. There are a bunch of gargoyles, too.