I think that if your looking to fly to DME in December book whichever fare is the cheaper, BD/BA. I think it will matter not as come December you will end up on a BA branded aircraft operating under a BA flight number.
Its unlikely that any slots that have to be given up as a result of the take over will be taken over by anyone (SRB) this early as it takes time to get aircraft, ops etc in place for new routes.
Most likely in my opinion is that you will see 5 BA rotations a day to DME until whoever gets the slots has an operation in place to operate it
cs