a NB not that bad honestly, in a 1k pt 3 way game, i took one out with 12 Fire Warriors. i do not see whats so good about it, altho the model kiks ass.
seriously tho, i would make the immortals one squad, take out the NB, throw in a lord with res orb, phylactery, and a warscythe. then with whatever points are remaining, add more warriors or sum wraiths/destroyers.
DF