http://www.uscis.gov/eir/visa-guide/eb-2-employment-based-second-preference/national-interest-waiver I had similar situation when applied for NIW (MS and did not have any publication). Last year my NIW application was approved.
agree with JoeF and pontevecchio. I had similar situation, i.e. foreign national, studied and then worked in the US for several years, thrn left the country. Applied NIW after left the country for almost 4 years and got it approved about 5 months after filed the application.