What will happen??
No one will have the BTC address. Hence will them isolated?
In FIAT, people can handover money to someone.. So, i predict BTC will be disappeared gradually.
A lot of people have died and their money (fiat) was lost in a pot in a garden or thrown away in some old mattress. It has happened and will happen no matter if it is fiat or bitcoin.
What you need to do is tell your family how they can get to your funds, and it holds with both fiat and bitcoin all right.