Finish the PhD. The PhD is training on how to do research, the topic is largely irrelevant. You have a fellowship and a supportive environment, which is just as good as it gets.
Apply for a postdoc anywhere you wish. My undergraduate degree is so different from my postdoc that people just stare at me when I tell my story :) in the department I did the PhD you could find architects, psychologists, mechanical engineers, physicists, mathematicians, epidemiologists, medics, chemists, microbiologist, economists working on the SAME project :)
Good luck!