Outcast's Path

Reinforcements should work in any case, unless you've killed everyone. By this time, you have Phantom Summon, Berserk, Blind, and other spells in your arsenal, regardless of the school of magic. Why not win even with a large army? Your army will grow to a considerable size anyway; just don't waste resources unnecessarily.

Added after 35 seconds
I'll reduce his defense now.

Added after 32 seconds
But I'll only do this on Medium and Easy difficulty.

Added after 9 minutes
Done =) Vadim_t, even considering the building purchases, you missed one more quest.