Dying unexpectedly, where does my assets go?

Say if I have no will, no relatives, friends anybody. Just a lonely old millionaire.

If my trip to Auckland took an unexpectedly turn and the plane crashes but I don’t die, but everybody thinks I am, what happens to all my assets? Lets say I’ve been gone for a decade, I had amnesia, stranded on an island, (like Tom Hanks in Cast Away). My house, cars, money, pets, etc. where does it go? Does the government take and auction it off to say it is for charity?