Severance package valid after 4 years

Hello, I live in California. I was laid off 6/27/2012 as part of a group of employees being laid off (I believe) and I was offered a 2 week severance package. I didnt sign it at at the time. I wrote an email back 7/18/12 with a counter offer. Their lawyer replied to me 2 days after saying my employment was "at will." Two days after that the lawyer emailed me saying the "agreement is withdrawn." I didnt replied to that email and a friend told me I could still execute the severance package agreement. Is this true? The document doesnt specify an expiration date or anything. Thanks! Pablo.