Suppose a Jewish woman converts to Christianity. Her children find out about their Jewish ancestry and decide that Judaism is right for them. Do they have to go through a conversion process? Does it matter if the coversion to Christianity happened many generations ago, and the decendents want to be Jewish (suppose the line is strictly maternal all the way down to child).
I don't think it's possible to convert out of Judaism. I don't have good source, but I would assume that a Jew remains Jewish and requires no conversion no matter what he does (ישראל אע״פ שחטא ישראל הוא ?)