A lot of company's over here have allowed their employees to keep their number/ take over the contract, have you asked anyone at management or higher level if you can do this. It really isn't that much hassle, just a form to sign and bingo.
If it is a case that the company has gone completely bang, just contact your service provider, explain the situation and they will give you the number as they want one more, not one less customer. let us know how you get on.