If BA were to offer a take or leave it deal - here's a new contact sign or at the end of 90 days you will be out of a job - then the individuals concerned will be under a lot of pressure to sign. It gets worse as someone that resigns from BA loses their ST entitlement unlike someone that takes redundancy. (I think they get their entitlement back at retirement age 65 but that can be along way off and during the years when you may want/need to have ST).
Of course there would have to be a period of time to allow people to sign. This would allow UNITE time to attempt to gain an injunction preventing the SOSR action subject to a full court hearing. In the best case SOSR would take approx 110 days from announcement to people leaving the payroll. They could effectively leave the company sooner as their airside passes could be revoked immediately and they can be sent home and given 90 days pay in lieu of notice. Whatever the case, this is not an instant thing, in law nothing really moves quickly.