Really good question! Not sure I know the answer. I dothesame thing with old courses. I never delete them, just move them to"Old Courses" and hde the courses. The certificates are still there.
But if you wanted to delete oldcourse, II would check it the old fashion way. Create a course, issue 1 certificate. See if i tappears in something like My Certificates block (any Certificate report outside of the course). Then delete the course.
I guess you could also look at the Certificate tables in the database. There is a scary move ;)