Dead-end job

A 'dead-end job' is one where there is no opportunity for advancement. It leads to nowhere, like a dead-end street.

Example:
-I'm afraid I may have to get a job at a fast-food restaurant.
-Well, it's pretty much a dead-end job, but hopefully it'll help you pay some bills!

He took another opportunity.

Saying that someone "took another opportunity" is a way of saying someone no longer works in a place. Since it is a vague response, there is no way to know if the person quit or was fired.

-Does Michael still work here?
-No, he took another opportunity.
-Oh, that's too bad! I really liked him!
-Yeah, we miss him, too.