They'll retire like pop stars
Returning as soon as it goes wrong for X times previous salary.
Saw it happen to a neighbour. He had coded nuclear power station stuff for Magnox facilities in some 50's language and 6 months later got a begging letter and and an invitation to write his own cheque until he had either delivered "start from scratch documentation" or the station was shut down, which was on the cards then and has happened now.
When he first retired he had a nice pension and his house paid off. When he next retired a few years later he also had a place in Spain, a narrowboat, and the resources to flit between them as the mood took.