And if they have no credit cards or closed them years ago?
Again, this only relates to people that have credit cards.
Yes, I think anyone with a US credit card should maintain it, but how does a US expat living in Thailand long term that has not had a US credit card for years hurt their US credit score?
From your link: "If a rating agency has not updated a credit rating quarterly or annually, then the last credit rating is the valid one. A credit rating does not expire. It's also important to note that rating agencies do not provide investment recommendations."
So, if you had a good score when you left, and have changed nothing since, you should have a good score when you return.