If you put the key in a bank safety deposit box...then maybe as long as the Executor of the Will isn't crooked or doesn't also have access to the wallet..... 
I think that it is good to give it or to keep it to a relative that you will definitely know like your parents, siblings or childrens. Bitcoin is a big thing today. We might not know what will gonna happen to it in the next few months or years but I think bitcoin will gonna be a big deal. If you die today and you don't tell anyone about your savings and private keys, it will be forever lost and will not gonna be retrieved eventhough your family filed something becuase it is risky to keep it and you need to have a secure wallet. So for me it ia good to have some of your family know about your bitcoin savings and private keys.