The NT tax code is only implemented for the financial year that you are BR so it will automatically be removed in Apr 2010. It will also be removed if you change jobs during this financial year.
The OR will contact HMRC and they will send your HR Dept an updated tax code. Instead of your work deducting income tax they will pay your wages, including the amount of tax you pay, into your bank account as normal. The OR will want you to pay the amount you normally pay as income tax to them so they can pay it on to your creditors.
There is no reason that you should lose your job and no reason that your HR Dept should ask you why you are not paying tax.