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.
It's none of your business, though... If that person owns number of bitcoins then it us up to him to secure the passwords and hand it over to his/her spouse just in case he dies... BUT if he doesn't feel like doing so, its none of your problems. If that is a huge amount of BTC then that's going to be a huge HODL! ha ha! Come on, man... don't waste your time with these kind of silly questions. Read some REAL articles in bitcoins so you'll get wealthy anytime soon.
The exception to this is when quantum computing or some other danger/risk becomes real. Lost/stolen bitcoins will be "redeemed" by hackers. Not by their intended recipients.