While in theory dwarven necromancers are great, they present a pretty major problem in that if they ever get involved in a big armed fight, they also generally mean a nearly instant fps (or rather, spf, seconds per frame) death when they suddenly get reanimating every single little piece of the enemy that ends flying around. It makes them pretty impracticable, specially in the military.
Instead, I'd propose one or all of the following, to keep their flavor, but help making them work:
- Reanimation takes more time and/or have a cooldown. Have them start at the largest thing in range, and then a noticeable wait before next thing (maybe 500-1k frames? Should make an reanimation per around 10-30 seconds). This alone should take care of most of the lag.
- Minimum weight to reanimate: Not only there's relatively little combat point in reanimating a very small left hand or something, having every piece getting reanimated means the game lags something fierce when a heavy battles means body pieces are flying around.
- It's a bit more of an accessory suggestion, not something that'd solve the problem on its own, but having undead decay and die on their own (at least on non-evil biomes and/or non-intelligent undead). They don't seem stay hostile against the next enemy attack anyway, so all they are doing there is eating the fps. Having them eventually die off automatically should help reduce the accumulation entities in the fortress zone. I'm thinking maybe a season or two, giving plenty of time, but still dying off in good time. Maybe have dependent on environment, with them dying off faster in good biomes? I know, dfhack already has a script for this too, but the software is not yet available for .50, plus, if I recall correctly, it also affects the intelligent undead visitors you occasionally can get.