Angryfool,
Even if what you say is true,I doubt very much the members will strike if balloted. It will not be an issue balpa will war over with the company and even if they wanted to,will not have the backing of the majority of it's members.
I believe BA have decided how they will crew the operation but do not go along with your assertion that balpa have agreed or indeed know. I think you will find that when the time comes they will decide what happens and have no need to negotiate with balpa. To negotiate would imply that balpa have some influence on key financial decisions the company makes.