Big Tudor - that would assume that the world economy didn't perform quite as badly as it did when Concorde was available - it did of course actually have a large number of orders, all of which were cancelled eventually. This included American carriers such as (I believe) Pan Am. Besides that I don't quite see how American involvement would have given it a difference career, since the costs were absorbed by the UK and French governments (which I am sure the US would also have done) and certainly the current state of United and American is a lot less robust than BA and Air France.
The rumour that is going the rounds is not exactly that BA will no longer keep it flying, but that if it came to such a situation such as losing its CAA certificate, then BA and AF would not bother to invest in ANY futher modifications.
The investment made post Paris certainly demonstrates to me that there was a certain pride in this aircraft, don't you?