A Thai widow friend's English husband died, his state pension was still being paid, not sure how long for, but she got a letter from DWP to refund the overpayment, think it was over 2000+ quid.
Long story short, ignored the demand, I think one more letter, then nothing, that was about 3 years back....π€
My English aunt was married to an American, he worked for an American Co. in the UK and paid NI in the UK, think for over 10 years. When they moved back to the USA, he was surprised to get a percentage of a UK pension until he passed away.....π€