I have a couple of HHKBs and fully agree. They’ve seen a ridiculous amount of use in the past 5 years and show no signs of giving in any time soon. Expect that if any part of it fails, it’ll be the USB mini-B connector.
I have an 11 year old and a 4 year old [HHKB]. Used/abused for 8+ hours/day, 5+ days/week. For the first 7 years of its life the first HHKB was transported to and from work every day, which can’t have helped it’s lifespan. Regardless they are still both going strong, though the keys on the older board are noticeably softer.