Once they cease to find you useful any longer, then you will not even get a polite goodbye!!

You and Drag are dead right.
At one place where I was employed, the management treated a foreign colleague of mine they disliked very badly once his services were no longer required. The old man was surprised by this cruelty and especially angered by the disdainful way the waiban treated him. As it was the week before the end of the semester, he guessed right that a replacement had been lined up in the wings. He knew he had nothing to lose, so he confronted his tormentor, and ended up having a swing at him. Unfortunately he failed to connect - the cowardly waiban ducked and ran away!