Attach account details to your Will in dead tree format
The best advice regarding this kind of thing I've heard is that you should document your logins / passwords / secret questions & answers etc everything needed to get into an account into a hardbacked notebook.
Write up your Will and have the notebook attached as part of the Will left with your lawyers. upon your death, no need for any tech company to know you are dead, your relatives will have full access to everything via that nice lil book enclosed with your Will.
Assuming you can trust your lawyers, the Will isnt destroyed by accident along the way or lost/misplaced etc etc etc but so far lawyers and the law seems to still have some respect for Wills & the contents therof and most tend to survive from creation to the reading of them.