There is a special relationship between aircrew (pilots/flight engineers) and aircraft. Without one the other is meaningless. No management wants useless hunks of tin lying about the tarmac bleeding the company of money. So they offer aircrew contracts consisting of money, benefits and promises in return for performance, dedication and work/schedule stability.
In this case it would appear that BA pulled the plug on the Concorde early. This has caused a material change in the expectations of the engineers and the promises made by management or implicit in their contracts.
As a result, the flight engineers would also seem to be equally within their rights to pull the plug on the Concorde. It comes down to a question of negotiating fair compensation for the early cessation to the careers of the flight engineers. The bargaining position of the flight engineers is diminishing by the minute and they need to work quickly.
Good luck and hopefully the last flight will be be on schedule.