I have had some luck with already tough dwarves losing (i.e. dark gray) hands, eyes, lungs, and sometimes arms. If they don't fall unconscious at the outset, they are likely to lead at least a semi-productive life after their other injuries heal.
Dwarves never heal from nervous system damage. Bad (i.e. red, yellow) nervous system damage will turn them into bedridden invalids, crippled or paralyzed. Minor (i.e. light gray, brown) nervous system damage will render them unable to spar ever again on top of occasionally becoming stunned or passing out unconscious for no reason. However, they will continue to practice at the archery range with crossbows, making them good fortress guards and royal guards (i.e. goblin fodder).
I have never had any luck with missing (i.e. dark gray) lower limbs. These dwarves are generally confined to bed for the rest of their lives. The tough ones will continue to squirm around, making them good bedridden kobold detectors for your entrances.
My worst recoverable injury was a hunter that got mauled by an giant eagle, cheetah, black bear, and sasquatch all on the same hunting trip. She was a legendary pump operator, engraver, and siege operator, and a decent marksdwarf and hunter. So all of her attributes were maximized.
She shot the giant eagle in the throat, but before it died, it bit off her left hand. She shrugged it off, along with her steel shield, and promptly fought a cheetah. The cheetah took three or four crossbow bolts and turned her entire right arm (i.e. shoulder, upper, elbow, lower, hand, fingers) red and her upper torso yellow. She ignored this as well and took on a black bear. She shot the black twice before it clocked her in the head, giving her a yellow head, nose, ears, and throat; and a light gray brain and upper spine. She also lost her left eye. She promptly fell unconscious. The black bear then turned her right leg (i.e. hip, upper, knee, lower, foot, toes) red and bit off two of her toes before her pet war dog sacrificed itself by biting out the black bear's throat, thus killing it. When she woke up, she started stumbling back home and encountered a sasquatch. She turned its head yellow with a good hammer swing of her crossbow, but the sasquatch punched her in the torso a few times, hard enough to turn her upper torso, lower torso, and one lung red. She promptly fell unconscious again. It continued bashing her while she was down, turning her right arm (i.e. shoulder, upper, elbow, lower, hand, fingers) yellow and her left leg (i.e. hip, upper, knee, lower, foot, toes) yellow before the other hunter in the fortress peppered the sasquatch with crossbow bolts and saved her. I was convinced she would die.
However, after seven year of resting, she recovered and resumed hunting. Though on occasion, she will collapse unconscious for a few seconds due to her missing hand, two missing toes, red lung, light gray brain, upper, and lower spin, and missing eye.