Write "Deceased" on them, then send them back. They'll take you off their mailing list. They don't want the cards falling into someone else's hands either....
I usually tear them up and throw them away. I have READ their " Offers" fine Print. 99% of them Have an Annual FEE, and many of them will give you a Limit of only $300.00 that is what they CHARGE YOU to get the Card. After you "PAY OFF" the $300.00 you will have a Card that is Worth $300.00. It is a Rip-Off Big Time.