Frontcheck - it's actually an EU legal requirement that customers are made aware of the airline operating their flight, particularly where this differs from the marketing carrier actually selling the seats for it. So, if services are to be operated by bmi, Lufthansa are obliged to disclose this to passengers booked and yet to book.
Once it is or at least IF it is confirmed, yes passengers will be informed, most likely via email something along the lines ''your flight is now scheduled to operate with our sister airline bmi british midland...'' I feel people are getting ahead hof themselves here at the minute because nothing has been confirmed on when or if this is definately going ahead by Lufthansa just rumour.