Based on the title of the topic "Would YOU..." I'm going to say no. If I were in the position of the original poster, I absolutely would NOT go back to school to finish a degree I'd started. Here's why:
A child w/CF needs attention from me as a parent. The child will do better having me spend my effort and energy learning how to be the best possible caregiver for his or her individual presentation of the disease.
Going back to school would take time away from the other kids, and use up financial resources that I may need elsewhere down the line for copays and other stuff relating to having a family with 4 kids.
Just as I didn't need to go to culinary school to learn how to prepare a nutritious meal for my family, I don't need to go to nursing school to be able to better deal with a child with CF.
Even w/o having completed a nursing degree, I know there's SO MUCH I'd learn along the way just by being a mom. Most nurses I've interacted with can't even pronounce half my medications, let alone understand CF.
Nothing would be worthwhile enough to me to abandon my young kids in order that I could go back to school. I think it would be selfish to do so. Any personal pursuits and interests of mine would have to take a backseat to giving my kids all the time and attention they deserve. I wouldn't want my kids to think that "what mommy wants to do" is more important than what they as kids need from me.