You know how to fix the braking system or electrical on an R143 subway car? Cause if they fire the union workers, we're going to have a lot of jobs for qualified people.
If the guy who does know is holding the city hostage, then it will be better for everybody in the long run to axe him, regardless of the short-term difficulties and expenses to do so.
IMO, union strikes are nothing more than economic terrorism. The same rules apply: No negotiations. Terminate.