It would be rare for a millionaire to have no will, but it does happen sometime because some people think they are immortal.
If someone has no will, and no legal heirs are found, it escheats to the state. That means the government takes it. This almost happened with the estate of Dora Mar in Paris, who was Picasso’s onetime mistress. Dora had hundreds of his paintings in her possession when she died- about 20 years ago. They were priceless. She had no known relatives, and no will. Just before the escheat, heir tracers who operate on a contingent fee, found some distant relatives (legally called “next of kin” ) in Argentina. The heir tracers got around 1/3rd, the heirs got 1/3rd and the State (France) got the rest (as an estate tax) for their Picasso Museum in Paris.
Everybody has distant relatives. Before money goes to the State, in matters involving over $10,000 you can be sure that the heir tracers will find & sign up some distant cousin to claim the assets/money.
I used to be in the heir tracing business. It was fun when I did it, but after 15 years, it got old, and at age around 30, I found other things to do. Maybe not as lucrative — but a needed change from that kind of stuff that made money, but had become boring. I got into other stuff like real estate.
This line of business is easy to get into. If you truly want to be rich and make serious money, it can work for those who work at it. I did it in the USA, UK, South Africa and Australia.