Airlines like Sabena and Swissair would still have gone under, the US carriers in Chapter 11 would again eventually have found themselves in that position still.
FD RJ and Avro RJX would likely have seen service, whether they would be successful in a crowded market is another matter though.
But don't underestimate the effect of that day, airlines were (well some were at least) preparing for the downturn, still they took a huge hit,
BA certainly did, you can plan for an expected downturn, no one was ready for Sept 11th.
Concorde probably would have flown until 2006/7, all 7
BA aircraft would have returned to flight, if not the 7th then certainly the 6th.
However,
AF may still have ended in 2003, which still would have been the end for
BA Concorde.