Commercially, this could be a difficult call for BA/IAG.
Acquiring bmi is a once in a lifetime opportunity to grow significantly at LHR. But it's not without risk and the airline would have to move very quickly in terms of stripping out costs and integrating the back office functions. I don't know whether bmi would technically sit under IAG with the BA brand licensed from BA, or whether assets would be transferred into BA.
Alternatively, holding out for LH downsizing bmi and disposing of slots would be a lot cleaner and without much risk.
I'm sorry to say it but I just don't think bmi has the brand recognition and clear sense of purpose to survive. In the absence of any growth at LHR, it is probably for the best that IAG acquires bmi to make BA a stronger competitor against AF etc. I don't see any other buyers stepping forward. Although the irony would not be lost on LH, from their perspective, they have a massive presence in mainland Europe and may decide that with BA, the LCCs et al, it's not worth trying to compete in the UK.