I'm not sure if its too late to comment about your situation, but it might be possible to petition your college instructor/professor for extra credit. If you failed by one point, usually in situations like that, its possible to work something out, such as writing a research paper on a topic that you and the instructor may agree on or something of that nature. I know that when I took my Anatomy and Physiology class at university, our instructor had some of his fourth year biology students hand out surveys that they assembled to aid them in their research for their thesis papers. For those of us that stayed after class and filled out the 20 minute survey, we got an extra 1 percent added on our final grade for the course.
I guess what I am trying to say is, exhaust all of your options, go to the dean, meet with a commitee of professors, whatever you have to do to get that diploma. Surely there must be someone in authority that can understand your frustration, background, financial committment and family circumstance that can cut you the smallest amount of slack.
The way I look at it, if you pass the RN exam, you qualify to be an RN. The college probably obviously understands that having the diploma allows you to write the RN exam. Not letting you finish your education after completing the diploma requirements, is in no way going to prove that you do or don't have what it takes to become a nurse. The RN exam will take care of that. Its no skin off the schools ass whether they issue you the diploma or not. They got your tuition money, and now are shutting down the program.
Fight for it! See what else you can do! Thats my two cents.