Invaders always used to be a renewable source of their metals, "goblinite". The best types of leather armors give an iron-grade protection, so once invaders come you could just drop the leather armor industry (except maybe for the wairpaintable central armorpiece) and start a metal industry out of the rusty iron goblins bring - IF you manage to kill them in first place, however. Elves will also bring you mithril bars at an affordable price, so you can even just go for mithril gear. Bones aren't that vital either, you can make furniture out of it, but you could just make it out of clay or wood without bloodshed. I'm talking about the mod's balance, not roleplaying here.
