Well. So that is certainly an interesting-looking map. I don't know if you lose after a certain point, it doesn't appear to be the case since you have no loss timer. First thoughts are that you could win this level by simply taking your time...Lots of time. What you'll probably need to do is amass a very, very large force before attacking any particular tower. The number of people you lose will depend on how quickly they can reach the tower and how quickly they can destroy it once they're there. Don't forget that you can always disband injured soldiers after battles so they don't contribute to your men lost later. Also, consider walling off the wolves once they've become aggressive toward you. Once they are moving in your direction, if you cut them off they'll simply disappear. That way you don't have to waste people killing them. Also, I'm not sure if this will be as useful, but you may be able to use walls to shield your people from some of the arrow fire up to 30 tiles away. For the first couple of towers, you will only have spearmen, but, you do have your lord. He can absorb many of the shots from the archers while your spearmen do the rest of the work. I think this is what Korsfarer Morgens was getting at when he said you have to think what separates a desktop commander from a good real-life commander.
Almost forgot - pikemen may be useful as they are actually more resistant to crossbow fire than swordsmen and slightly faster. They still do fairly well against archers too.
I'm curious, how far have you gotten through the level so far?
It's also possible that this map was just designed to be impossible and taunt you.
Actually after doing some experiments, I have found out that peasants which get killed do not count toward your troop death count. If you really want to win, you could knock the game speed down to 10 and disband any soldiers which are about to die when you attack.
The pikemen approach seems to be going quite well so far. I've cleared out all the towers on the left and right. I think the number of pikemen killed (with disbanding of the ones under fire) is less than 20. I estimate I lost about 100 spearmen clearing the left-side towers, so, doing this seems to bring the goal at least within reach, although it still seems like it will be difficult to achieve.