Nope. Resource system works like this:
You place a building in your city. Every fifteen seconds or so, it gives you +15 "resources" (indicated by a barrel. So, apparently, the only important thing in life is getting stone drunk). After it's done this a hundred or so times, it now makes +21 (or so) resources every time. It does this a couple times and then stops in its fully-upgraded form (buildings are upgraded by use, a mechanic that I fell in love with very quickly).
It is utterly impossible to deplete resources so long as you've still got one of those buggers chugging away. Evil races can get an extra boost by building lumber camps and harvesting nearby trees, and those DO run out, but they still have a few slaughterhouses or furnaces to keep the war effort going.
And besides, both of these guys could create basic infantry units for FREE. An orcish warrior squad only costs the time to make them and the population space. No resources required.
I really don't know *what* happened. I think it's possible the "AI" basically just had a checklist it ran through when building units or doing stuff, and it eventually just ran dry. Seems like a stupid design, but I really don't know what would cause an AI player to begin utilizing "Sitting Duck" style combat.
EDIT: Also, this is getting dangerously off-topic. Err... Titan Quest? It's pretty much Diablo II 2 (I actually thought I was playing Diablo II at one point, before I saw yet another moon clan satyr die and go ragdolling across the landscape), so there's not really a whole lot of the "horde" aspect...
I can't shake the feeling that I've played one of these things... Damn annoying not being able to remember what it was.