My sov also gets death magic.  Infecting everyone with blindness goes a long way.  I also like to give her that staff of souls that increases spell damage and lets you generate mana with kills.

Never watched "Trainspotting"?  Great movie that.  Heroin is a class A narcotic.  Mainlining means injecting it into a major vein and is associated with an intense feeling of euphoria and pleasure.  I was using that as a metaphor.

I would take Air by itself over both Fire and Death.  

Also wouldn't need Death Worship anymore if you have Air, can trade that for a more powerful choice as well.

Procipinee's Crown is worth having. Have a free army of summoned units, for example.

Fire is fine as far as it goes but I'd always prefer Air for Haste, Guardian Wind, Cloudwalk, Titan's Breath. Sure you need a different way of winning battles to Fireball, but there are plenty. Fireball is quite an expensive spell which takes two turns. Haste is a cheap spell which takes one turn. Titan's Breath is a battle winner on its own. With -1 casting time and/or a very high initative mage it's pretty much an exploit in that you can beat any AI army if you have enough mana and a few units to damage prone AI units.