I just had miles refunded yesterday for a booking originally made in 2019 (!!), which I subsequently changed numerous times, and eventually cancelled in July 2021 (yes, it took 8 months and many frustrating phone calls to get the refund processed). Needless to say, most the miles had expired, some time last year. So when the miles finally reappeared in my account yesterday, >250,000 of them were immediately wiped again.
However, I called today, and despite a lengthy wait before I got through to an agent (40 mins), it was resolved quickly and painlessly once I got through. The miles are now back in my account, with a new expiry of Sep 2022, and I understand they will be automatically extended for another 6 months if not used by the end of Sept.