Light for the Necromancer.

I must disagree with you here! Magic is not tied to ideology in any way (and even the connection with races is quite relative).
Overquoting

Firstly, when the game reaches a very late stage and the armies become very large, then summoning and chaos (especially) become less effective, while darkness and light come to the forefront. Therefore, I don't see anything reckless in replacing summoning with light. Although, indeed, Necropolis often already has mass slow and sometimes mass stone skin... (maybe the best option is to stick with darkness?).
As for ideology, I believe that divine retribution is not strongly associated with necromancers, although, in principle, neither is empathy...