Last Well? What is my legal right ?

My husband write a letter for me that if ever he die i well cremate him and ask me not to tell anyone . he would not let the US immigration know that he already died. so that i can use his debit card for 8years. i want to bring the letter to the lawyer and notary them. Im the legal wife and married to an american man , do think if let the lawyer notary the letter and bring to the US immigration and show the death certificate. do u think i can still contenue is pension monthly as the legal wife?