actually.. you CAN kill him.. it's just DAMN hard coz he has SO much life and kills your units with about 2 hits and your heroes with like 3-4.. i would say it's impossible in hard to beat that map this way.. but in normal it's doable.. i've managed to kill of his town and "peasents" using my flying units to hover and do hit and runs all the time.. this was probably the hardest part of it all.. doing that constantly as i had to organise and build defences etc.. create wisps and 2 more camps near the 2 other goldmines.. move the start up camp down to the orcs.. and creating unitz like a nut since they kept dying all the time..
when i manages to kill his hero gate the first time i was SO happy

.. then a pesky bunch of monsters came and took out all my flying units near it.. luckylli i had a bunch more on the way.. and since they where weakend i managed to destroy the under work hero gate.. then i aimd all my fire on him.. just for the hell of it.. and it indeed did take some life out of him.. so i continued.. i had monsters all over me.. and he had allready killed off the humans by the time i had revived my heroes.. but i waited since my camp was with the orcs now.. he would come to me.. so after beating most of the undead monsters attacks.. and managing to blow up some buildings.. i used my heroes to slowly lead him into my night elf/orcs camp .. where i had built mega defenses.. so that when he got there.. he was mostly killing my boulder tossing trees

.. and well.. his minions are strong (not as unbeatable as he is but very close).. but i made them all spread out.. and then had groups attacking each one with a litle bit of everything at the same time.. he must have spawnd about 15 huge monsters b4 i managed to get close to killing him.. and then he somehow suddenly had more life again.. so i'm not sure but i think he regenerates mana into life or something like that.. so it took a long time to kill him..
i'm not sure if it was luck.. but he managed to kill pretty much everything i had by the time he was dead.. i managed to survive coz of my superior amount of money and my hero gate being still up.. and using vines on his coming monsters to trap em and kill em b4 they killed me..
after i killed him.. i had pretty much nothing other than my hero gate.. a towntree.. and a few wisps.. and a bunch of money from the 3 gold mines.. still.. for a while there i was sure i would be completly overrun since alot of the buildings he had where still up.. and some more peasents where coming out.. i managed to kill and destroy most important buildings b4 his troops got back though.. since his town was still very limited and had terrible defences..
the only thing to fear where the dragons.. but i managed with some archers.. a good tip is to try and make sure his "woodpickers".. don't collect much wood.. since you can use the convert to treetroll spell and use them against the undead instead.. i used it a whole lot.. also.. make sure all your heroes are at lvl 10.. with all their magic abilities and some type of good equipment.. or else this is just not gonna work.. also hire alot of monsters from the merchants

.. and one last thing.. use the life fountain.. put a bunch of trees around it.. and keep it closed off so he can't get life with it but that your heroes fitt in there perfectly.. it'll make them survive for a couple of more hits than normal

.. now everyone try it

.. good luck..