Honestly, you don't even need to deal with the demons roaming the map... unless, of course, you want to level up your hero.
I breezed through this mission using... excuse my language,... a "mother of all spells":rolleyes:. My Arantir had an unholy word. One word and the garrison was gone...:eek:. Or half the army. The rest were finished off by archliches and vampire princes:smile19:.