To answer OP's original question, I think that a lot of people in 2002-2003 were thinking that individual Concorde aircraft would last until their D-checks. It's an answerable question as to when they would occur, but I don't know when they would -- maybe around now.

Of course, there could be other intervening events, not fully known in 2002-2003, that could have ended service before the D-checks:

1. The subsequent rise in oil prices would undoubtedly have put additional pressure on Concorde, so who knows at what price point of oil Concorde might have been shut down, or just suspended.

2. There were also a number of individually small to moderate events -- such as a few flights losing chunks of the rudder -- which could have at some point brought Concorde to an end before the D-checks.

Meanwhile, conspiracy theorists propose that AF badly wanted to end Concorde service but could not stomach the sight of them discontinuing it while BA continued, so they pressued Airbus, the supplier of spare parts, etc. to raise the cost to a prohibitive level for BA.

While I think this view is extreme, there may be grain of truth in it -- recall that AF ended service in May 2003, with little if any fanfare, while BA maintained its scheduled service through October 2003, when its operating certificate for Concorde expired, and in the meanwhile flew a number of final flights, goodwill flights, etc. to a variety of other locations.

The loads also bear this out -- I want to say AF had flights with 20% loads routinely, and BA was maybe half-full.

I was lucky to do two roundtrips, one in 2002 and one in 2003 after the retirement announcement, using mile largely earned from Diners Club and the 2x conversion rate promotions. BA earned incremental money off the likes of me, but there's no way that half-full planes, where a number of passengers were on discounted fares, using miles, etc. could justify continuing it.