The simplest solution I could find was to delete the parent directory from the working copy (with rm -rf, not svn delete), and then run svn update in the grandparent. Eg, if you deleted a/b/c, rm -rf a/b, cd a, svn up. That brings everything back. Of course, this is only a good solution if you have no other uncommitted changes in the parent directory that you want to keep.
Hopefully this page will be at the top of the results next time I google this question. It would be even better if someone suggested a cleaner method, of course.