One case of somebody faking their own death was adult film actress Hyapatia Lee (aka Vickie Lynch). It was publically announced she had died of diabetes in 1998. It was later found that she was alive.
The motive was never clear. There was a financial aspect - she had set up a charity for people to donate to in her memory and the sales of her fan memorabilia increased after her “death”. She also told people she was being stalked and had faked her death to fool the stalker. She had apparently also become unhappy with the adult film industry and may have been attempting to make a clean break with her past.
I’m guessing that anyone who is seriously wealthy is going to have lots of different assets (bonds, houses, bank accounts, stock portfolios etc.). Most likely they will have them scattered all over the world for various reasons, and shuffle them around regularly. Over the course of a few years it would probably be relatively trivial to gradually divert a goodly proportion into various secretive offshore locations, or just into perfectly ordinary assets registered in the name of Bill Jones, formerly of Phoenix Arizona, currently of Singapore or wherever. As for traceability - not if you have a leg-man who knows what they are doing, and a big enough shell-game to hide the transactions in. Similarly for ID, not a problem. After all, the idea is to still be a millionaire at the end of the day, and millionaires are not usually short of people willing to do them favours.