I agree that SOSR might be less likely but I don't think it would be too difficult to prove that if the current (and last) offer is rejected and the company lurches back into IA then the losses would be significant. SOSR doesn't have to be based on the current position, merely the position that might occur if the action is not taken out.
BA could argue that they have tried to negotiate, gave concessions and were met by intransigence. If the eventual outcome is going to be significantly damaging in terms of IA or even loss of revenue through threat of IA then I'm sure they could find a judge that would agree that it was necessary for survival of the business.
Personally, I don't think this will happen. If BA haven't used it already (and by God, they must have been tempted) I don't think they will. I think there will simply be an acceleration of MF and no say so of the transfer of routes etc so the "legacy crew" will simply wither on the vine. If this offer is not accepted I would be amazed if in 2 years time MF were not doing all "premium" trips. Happy days.