Turtle Controller
In the short term, I agree with you.
In the long term, I think you've answered your own question.
As you say, anything can happen including entities like TCX being brought into BA/IAG. You never know. AA/BA is a major TATL Joint Venture and it would be a surprise if they gave up on connecting the largest US market with the second largest U.K. Market.
I'm not saying there will be some seamless transition, or that there won't be a gap in service. There almost certainly will if AA pull out for S18.
What I am saying is that the MAN market continues to grow, BA continue to loose gross passenger numbers ex MAN (let alone retain market share) and it would be strange if they effectively left that market to others.