I'm not an expert on NRMP rules or how strict people are about them, but here's what they say:
http://www.nrmp.org/policies/the-match-commitment/
If I were you, I wouldn't do anything drastic just yet; you should consider talking to fellows at the program where you matched... how are the 2nd or 3rd years doing on a career search? Is it a supportive place? Is there a possibility to stay on as faculty?
The main difference in the Match results this year seems to be that fewer foreign grads applied and matched (only 107; in the past it was over 200). This is because it is very hard for ppl with a J1 (and sometimes foreign grads in general) to find a job in nephrology. For US grads, the number is lower, but relatively similar to last year 79 matched vs ~90 last year. You can still get a job and have a career in nephrology, but it's just hard to do so if you have strict geographic lmitations, and starting salaries are usually lower than for hospitalists. Final salaries depend on your partnership group structure/success, and can exceed those of hospitalists (assuming the hospitalist is not moonlighting too on off weeks). Lifestyle also depends on your group: I.e., tiny group and you may get q2/q3 call; I've heard of large groups getting ~q6 call.