I was laid off in December with no written return to work possibility, but they did say that if things picked up they would be able to call me back. Among the 5 laid off 1 was over the age of 40, 3 over the age of 50. We all signed the paper in order to receive our severence pay.
Employers are generally under no obligation to offer a terminated employee a severence package and when they do it generally contains a clause that if you accept the payment offered you agree not to sue your former employer for any reason known or unknown ( in california that is CC 1542 ) .. so they are buying the peace.
Also you are generally advised that you should have an attorney review the document before signing and that if you do sign the document you have 7 days to change your mind. .. at least in California.
Review this with a local lawyer familier with Employment contracts and severence agreements.