I hear of more and more schools doing away with pinning ceremonies (or, at least, telling the nursing students that, if they want a pinning, they have to plan and pay for it themselves) -- I guess this is one of the "down sides" of college/university depts. of nursing as opposed to hospital-based diploma schools (where the pinning was the graduation ceremony).
I can see how the school would feel (and, I must say, I agree with them) that you are earning an academic degree, the same as every other graduate of the school, and the ceremony which recognizes that is the college/university-wide commencement ceremony, same as all the other graduates. After all, the education majors don't have a special, private ceremony, or the math majors, or the English majors, or the chemistry majors, or ... (etc., etc.)
I am an old diploma grad (who has since completed a BSN and MSN, so I am definitely an advocate of higher education in nursing!) with v. fond memories of the pinning ceremonies at my alma mater, inc. my own pinning. However, if nursing, as a group, is going to say that nursing preparation is a degree like every other undergrad degree (which is basically a good thing, I think), then one of the consequences is that we're going to have a harder and harder time convincing administrations of colleges and universities that we're somehow "special" and different from all the other departments of the school, and deserve special treatment ...
I do agree that your school handled this situation v. badly, esp. on such short notice. However, it is true that you're not graduating from a "nursing school" as a separate entity; you're graduating from the college/university, same as all the other graduates -- it just happens that your major is nursing. Go to commencement and receive your degree and whatever recognition/honors you may have earned, and, if the nursing students want to get together and do something social with their families, you can certainly make whatever plans you want to do that.