I haven't had this happen to me as a writer yet, but as a reader, I have to agree with Mare about keeping your stories up. It would be nice to post an author's note on your unfinished stories, warning readers that they may never be finished, so new readers can decide whether or not to check them out... but old readers may want to reread what's there, whether it gets finished or not. And definitely don't delete your finished stuff... I hate when authors do that!!!
Plus, you never know... a few months or even years from now, you might change your mind and decide to come back, and then you might regret deleting stuff. Good luck with whatever you decide!