Ah, it's intended to be winnable. It's possible that it may be very hard if you are lacking some bond 6 morale skills and  if you are not countering factions/elements with your units? If you are finding it impossible, I will consider lowering the difficulty. I scaled it more on my own playthrough so I, uh, probably have a biased perspective XD;;; please let me know a bit more of your specific troubles if you are still struggling.