Girl I hear ya!!! The back of my hair fell out last year twice! The first time, it was the back part close to the neck (nape), why? Because the stupid stylist did not wash out the relaxer out of my hair properly. So the hair fell off gradually, ( at the end, the hair was less than an inch). But, being that I have a lot of hair, my other hair covered the area, and it was all good. Second time, when i moved to philly in september, i went to this other stylist who used vitale, well my piece, the hair from the left side back of my head was falling out in her hands as she was washing out my hair. (she attributed it to the dryness of my hair, well, i think that if she is a hairdresser she should have said something such as "we shouldn't relax your hair now, or we shouldn't use Vitale because it is a very strong relaxer) I was scared like HELL! I never went back to that place. My hair was jacked up, but I was still able to cover it. I went to another stylist, and she cut the rest of my hair up to my jaw. I am still covering it.
Don't cut your hair!!! I regret it. Just cover it with the longer pieces of your hair. Roller set it or do straw sets/flexi rods, because that will hide it too. When you wear your hair up, just put pretty clips in the back where its short, to keep it up and to make it look neat. Do not cut your HAIR! Sorry that I am so passionate about this topic, but its just i hate that i cut mine, and i am tired of these short pieces in the back.