Professor Brier says those long reigns were usually followed by a collapse, because the Pharoah was too old to keep the state functioning, but couldn’t be replaced until he died.
If that were true, it would have happened after Pharaoh Pepi (reigned over 80 years), after the long reign of Rameses II “the Great”, etc — Brier has it wrong, it’s typical for the longer reigning monarchs, pharaohs, emperors, etc to be at the beginning. It’s not foolproof of course, but e.g. Elizabeth I of England left no heir of her body; her heir was her cousin James.