Should I negotiate my severance? (update)

My manager said the package is final, but the letter gives me time to review. I would rather hear the honest version than the polite one. There is a non-disparagement clause. Should I see a lawyer?

An hour with an employment lawyer cost me a small fee and made me feel much safer about signing.

Ask for the offer in writing and do not sign on the spot. A day or two to think is normal.