Isn't this problem already solved in the non-tech world through a last will and testament or a bank lockbox which contains passwords you want people to have in the event of your death?

I'm not sure it's a perfect solution but might be better than counting on someone to reverse engineer or hack into your phone.

If you're serious about encryption you should always have a backup key somewhere... unless you want a single point of failure (you). Both should be an option.