I don't see what BA cabin crew can do to avoid Columbus.
BASSA have already allowed temporary contract cabin crew. BA simply need to make all future cabin crew recruitment temporary contract. Then when numbers are great enough, and their contracts expire, they are offered jobs with the new outfit. When mainline cabin crew strike, the new outfit has sufficient numbers to keep the operation going, and the action will be rendered impotent. It is precisely for this reason that BA pilots were/are worried about Openskies. BA already has it's openskies for the cabin crew, through the acceptance of Gatwick T'c and C's and also the ability to recruit temporary contract crews. And now BA has it's Openskies; to play the same trick on the pilots.
Each scheme will take a little bit of time, but reduction in flight and cabin crew T's and C's within BA is going to happen, whether we like it or not.