I have always assumed that transfer of 'customer base' (as much as you realistically can) would be part of the purchase. I would also assume that their will be a clause on status matching being banned by M&M for a period for UK members.
You wouldn't buy bmi unless you were getting the customers with it, and the way to do that is that BAEC get DC.
Dreams of M&M were always just that in my book.
I wonder if they will offer to change my US reward flight to BA. No availability on BAEC but it must be cheaper than writing a cheque to LH (going via FRA as most people seem to have to do these days).