Ditching small planes has something like a 90% survival rate, and that includes planes that ditched in much worse situations.

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?