Or it's an insurance scam because the owner needed some cash. A staged accident in the middle of an ocean is a nice way to pull that off.
These are not unsurvivable forces we're talking about.
For example, to ship a new Cirrus SR20 to Australia starts at $28,995 and you'll need to wait for factory reassembly and certification. To ferry the same aircraft costs $22,800.
For someone in a bad enough situation that they are willing to commit insurance fraud by faking a crash, it probably is a pretty good risk.
See this earlier comment for a link to data on small plane ditching: https://news.ycombinator.com/item?id=8957313
That said, insurance companies aren't stupid. Would they really let the person insure the plane for so much that it is better to lose it for insurance than to simply sell it?