Lost assets when someone dies happens all the time, especially with overseas bank accounts. if the person doesn't share those details with a trustee then yes its possible that the assets remain dormant. Bitcoin is no different. The same way your will have everything else shared with someone you trust, you should do the same with your BTC
Bitcoin will never die because the owner dies. You can have the bitcoin of that owner if he said his account to you. The owner must share his details to his beneficiary for transfer of bitcoin to another account or user. Like banks, you will never get the bitcoin of the true owner if you dont know the owners account
I don't know what is the purpose of the OP why he asks this, blockchain is not in the hands of the owner, so whether he is here or not bitcoin will surely continue no matter what so, don't worry about the obvious things like this.