I just want to adress something repeatedly mentioned in this thread; the high cost/pyrrhic victory for the dwarfs. Had the mountains not erupted in massive earthquakes and volcanic eruptions, killing thousands and enormously damaging the dwarf holds and defences and leading to the time of woes and goblin wars, it'd have been a fine victory for the dwarfs. The war was costly in that they'd probably have had to give up on some territory on the plains (present day empire) to the humans, at least for a while anyway, but had the mountains not been shattered by the slann/skaven machine, the dwarfs had returned to their holds and eventually recovered, and life would've gone on. Even when embroiled in a massive war against the other most powerful nation on the warhammer world, the greenskins and skaven were virtually no real issue despite being occupied for 400 years of war. Then the war ends, couple years of steady recovery (60 or so), > wham < earthquakes, apocalypse ensues, greenskins and skaven invade and capture several dwarf holds. I think that without the war of vengeance this cataclysmic disaster would still have screwed over the dwarfs. Portions of holds were filled with lava, for heavens sake!
Gunpowder would not have changed the outcome of the war, merely turned the balance slightly further towards the dwarfs. It sure would not suddenly turn into an easy victory though.
Basically think of the inclusion of gunpowder into the war of vengeance like this: imagine the war, with all its battles. Now increase elven casualties of each battle by 10-15%'ish, slightly decreasing dwarf casualties. Killing the enemy alone doesn't win you the battle/war. Any war with skaven or goblins should prove that. However more easily killing the foe allows you to lose less soldiers yourself and gain slight advantage in the following battle, and the next and the next and the next, and if the high elf casualties had consistently been a bit higher due to gunpowder, and the dwarf casualties lower due to the killing of opponents that would've killed a dwarf had they been alive, dwarfs can simply steadily gain an advantage in every battle and every following battle, making the entire war on the whole more tilted towards the dwarfs as every single battle is slightly easier to win. Killing the enemy, or winning battles alone doesn't win you the war, but I doubt that the elves losing more battles in a war that they eventually lost anyway is going to do them any favours, especially when artillery and handguns heavily counter 2 of their greatest assets; knights and dragons.
If it would be such an easy carefree solution to problems, I think they would do it more frequently Certainly after fighting a war for 400 years.And whos to say that such an intervention as black powder wouldn't have begun an arms race to get the a-bomb?? The HE may have been forced to do the reckless again and draw the sword of khaine again...