Question

My husband got fired from his job. He is being accused of theft. The day his ex employer fired him he had my husband sign a document stating why my husband was being let go, that he wasn't going to pay him his final check and that he wouldn't press any charges. They both signed and dated the document although my husband was under distress when he signed. Since his ex employer was not going to pay him his final check he was going to go through The Bureau of Labor and Industries to fight for his check. He let his ex employer know he was going to make a claim. Then 3 days after my husband was fired his ex employer informed him that he was going to press charges.
My husband received a copy of the document along with his final check. We are wondering if my husband were to deposit his check will that void the document that they signed and give his ex employer any grounds to press any charges?