I work in a white collar world and manage a team of engineers. If someone says they want to leave, I assume they mean it and they're not bluffing for money. I tell them they should go where their heart points them, and that they will be missed, and move on. Because in the end, if his/her heart is not in the team I've built, they're not going to perform, and we should separate and move on. No need for bluster or confrontation.