This is a case by case basis which depends on your employer. It is probably more desirable to the company to keep you happy and give you back your vacation. You should talk to the HR department to find out what your company's policy is.
One important thing to remember is that if you have been laid off and you had saved up vacation time that you did not use and the company lays you off, they are required by law to compensate you for that time. They need to pay you for any vacation days or hours that you don't use at your salary rate. So you might want to decide if the money or the vacation is more important to you.
