What would BA do with BMI? Certainly they'd buy it for the slots - but slots that aren't used are forfeit fairly quickly, I think, right? So they'd have to buy and absorb bmi, as they wouldn't be in a position to operate those slots immediately. An added impact of this is that I suspect that bmi pilots are still cheaper than ba pilots (cost saving) although bmi cabin crew are almost certainly more expensive than the recent round of ba cabin crew on MF.
It would actually be in the interests of the work force for BA to move quickly to buy the whole lot, as they would almost certainly have to start off by being absorbed in this way - in other words, job security at least in the short term, and probably protected terms and conditions as well. BA would be buying it in the knowledge that it was losing money, but on the basis that within three years, the money they could make by getting another 11% of slots at LHR, with the additional leverage of their position at LHR and their much better brand identity. (Think about easyjet filling up aeroplanes with high density seating on routes that GB was losing money on).
Incidentally, I wouldn't pay too much attention to the losses made prior to Lufthansa. The airline was largely owned by Michael Bishop over that period of time, and he didn't seem to be noticeably sliding down the Rich List. In other words, whilst from a declared accounts point of view, it "wasn't making money", it was actually doing okay. In particular, post Star Alliance, with Lufthansa underwriting losses that mainline made, what was the point in that part of the company declaring a profit? It would just reduce the income to the group.