When the British were suppressing the Thug (stranglers) cult in India, they had the same problem--what to do with the most fanatic members of the cult. In the end, they were unable to release some of them, and had to keep them locked up until they died.
Probably might have to do the same here.
Being fanatics, they don't fear death much. However, they do fear living the rest of their lives in a cage while worrying about what their women are doing in their absence! Keep 'em locked up forever.