I am not sure what you want. Do you want the last page of chapters to be numbered or do you want them to be completely empty?
I want even numbered last pages of chapters which have no text or images on them to be completely empty. I tried various versions of the code for "Truly empty page breaks" at http://wiki.contextgarden.net/Titles that Jörg's message about \definepagebreak led me to, and I tried various versions of the additional discussion about "Again: How to make empty pages by default empty?" from November 2003 in the NTG-context archives. I couldn't make any of that work within the last half hour or so. Thus, I have now changed my macro which begins chapters so it turns off page numbering before the \chapter call and turns page numbering back on after some text has been place on the first page of the chapter and that now does what I want. So, that's kind of a brute force approach to getting these completely blank pages "automatically." Thanks everyone for your suggestions. -Dave