There is not simple answer. If its top kd and they can win cow n1 but cant win n1 for kd stay in war for longer is good move to can win at least cow. If its early age and your cow can grow and rest from kd will be crushed its good move again. All provs can find easy land after war is over for grow again but cow cant, so its better for kd. If you are in ghetto and you have 2-3 active provinces and you loss this war because all are inactive and so n00b, noting wrong cow to keep war for longer and gain. At lest he play and have goal. Rest are just free food don't matter if kd are in war or peace. If you have active ghetto and cow cant finish top 3. There is no point to stay in war when you loss clear.