Not long after bragging about those brakes with 27000 hours a wheel cylinder failed just like you mentioned. Sitting overnight, it leaked all the brake fluid out. I tore it all down and the shoes were 3/4 worn out. All new shoes, wheel cylinders, and seals were installed. The master cylinder is doing ok.
The Toyota owners manual says the brakes should be inspected once a year.
After neglecting the brakes on that truck, I would suggest new wheel cylinders after 5 years or 10000 hours even if they don't show and leaks. The brake fluid was checked weekly and it was not dropping down. All of a sudden, overnight, that wheel cylinder just let go.
It is one thing for a truck to konk out and not run but a brake failure is something no one ever wants to happen.