Do not sign the severance. That is an ironclad legal document. You will have no rights after you sign. Go to the Department of Labor and report the failure to give WARN notices. UNH will be fined 2-3 months pay with interest across the board. HR Direct are a bunch of Dimwit numb skulls. Assert all of your Title 7 Rights. What you know is worth much more than the severance. Stop being led by a bunch of crooks!
Reposted from @NsyddcT-61fio for good advice.