In the early 1990's British Airways decided that they wished to cancel the last remaining 40 pilot training courses at Prestwick, but were informed that under the contract they would have to pay for them anyway.
This led to BA offering those places to Flight Engineers who were under a certain age and who could meet the entry requirements.
Other than that there has not been any other F/E retraining schemes in BA.
As to the Concorde F/E many of them were encouraged by BA to leave the 747 fleet and convert onto Concorde, as due to their age they would be able to see the Concorde out to it's projected retirement date of around 2007.
This meant that when the Classic fleet was retired, they did not go after the jobs that came available elsewhere and which are now all filled. So yes they did know that the F/E job was coming to an end, but stuck with the company to ensure that the Concorde could continue flying, so perhaps BA does owe them something extra now that Concorde is to be retired early