I agree. This is a once and only chance for LH/*A to gain a substantial presence at LHR. I just can't see them letting go of it.
However, if there are discussions on whether BA can buy some slots (assuming BA would be able to buy or want to buy?) could this be a prelude to BA moving to Star?
If LH want to offload some slots, BA is an obvious candidate to buy some of the less lucrative slots because it has such a large operation at LHR it can make use of them. Other buyers are probably only going to be interested in the lucrative slots for long-haul ops that LH would want to keep.
BA joining *A is highly unlikely.