What skills should Necromancers take when facing Orcs on a very large map?

Well... you can deploy Shamans, but would you agree to replace the reasonably decent Daughters of the Earth with the less effective Daughters of the Sky in the late game? And besides, a Necromancer might harass you.

And imagine if those same Goblins, which the Shamans use to generate mana, are simply killed off? What will you do?