[JepSan]

You are right about mages typically casting other spells when there are no appropriate targets for the scripted ones. Your bless spell will not be cast if there aren't any blessable troops around and the tangle vines has a short-to-medium range (about 25 squares i think). If there aren't any enemies within range your mage will use a different spell/action. He will not proceed to the next scripted spell until the next turn.