I have to wonder how this would go between three factions.

The Horde might jump in if it looked like the government was in peril because their free ride would be over. Then again they might let a power vacuum manifest so they can force sharia, and they're not above going door to door to clear out a city to make it theirs if they have to since they're still using the 7th century playbook. I wouldn't doubt there are groups who would be very happy to start arming them if they say the word.