That is not the first time I've heard those words. Saying "you will never work here again" is almost like when Ringo points a gun at Jules in Pulp Fiction. And Jules said something like "I don't want to disappoint you but this is not the first time I've had a gun pointed at me".
For whatever slight, somebody who thinks they're in power over me likes to take the attitude that if they have anything to do with it I will never get another job in the place again. And yet I still work in the place. A cockroach. And I leave when I choose to leave.
I think it's mostly because those people move on as well and I become peripheral to them. And I'm sure they think that they are moving upwards. Perhaps they are.
But in about 18 years now of working in places where some people just really don't want me, I have come to see a pattern. The people who think they control me can hate me or love me. But if I provide value for the company's customers then they sure as hell can't ignore me and it's hard for them to get rid of me.
And the cockroach survives.