Maybe if you make dwarves impossible to be raised as undead. [ITEMCORPSE:xxxx] like with bronze colossi might be your friend. Won't help against necromancers, husks and assimilated dwarves leading goblin squads, but those aren't that numerous.
i suppose this could work, but i would need to regenerate a new world where dwarves could not be raised as dead by adding the not raiseable as undead token to them so necromancers cannot raise them in world-gen.
this presents some problems though, because atm i have it so dwarves have the same starting biome as all other races, and they tend to be quite numerous during world gen. And i would need to find a way to limit their population (like by changing their starting biome back to mountains, but my worlds tend to be huge islands of prairies and desert) without causing too much rejections due to un-playable civ. My aim in world gen is to generate as many towers as possible, making dwarves impossible to be raised as undead makes this harder for necromancers to get their armies up and running.
I also dont want to restart because this fort shows promise and is one of the few embark attempts to survive a terrifying embark's first year (with necromancers trying to kill you the first summer and fall).
Most importantly, making dwarves non-undead candidates defeats the purpose of a terrifying embark, where the dead-island theme is the main attraction; my dwarves will not rise as undead and cause fun when they die any more.
for the problem of world rejection due to lack of dwarves, i've found that dwarves require neutral mountains in vanilla, never evil or even good mountains, there is no ANY_MOUNTAIN token for starting biome, any ideas on limiting the number of dwarven civs so there is more tower fodder for necromancers, but not so much that there is world rejections? neutral mountains are a extreme rarity with my current setting as mountains tend to be medium to large biomes, and most of those tend to be evil.