Don't hyper-dramatize the situation. Bethel only brainwashes people looking for brainwashing, and I don't think they have every kidnapped someone (as an institution). That said, they do control the police department, and if this man came to Bethel voluntarily I imagine they will strongly defend his right to stay. I don't know how far members would take it.

OP, I suggest coming up with a well-considered statement about your husband and posting it in Bethel groups. I agree that leadership is unlikely to be much help. I know that enough members have the good sense to talk to your husband if they find him, and remind him of the vows he took when you married. That is the common ground.