The Roman Catholic church will stop supporting the BSA. That’s a whole bunch of scouts. I see no other course. Active catholics will make sure of that.
The Columbian Squires already have a structure in place, and with some modifications, could serve as an alternative.
http://www.kofc.org/un/en/squires/membership.html
They should go further. The Pope should threaten to excommunicate any Catholic associated with the BSA.