Lewis did retire and did get bored.
Hatahway was a very bad lead dective and boss to his very nice female sargeant.
Then there was a staff shortage of something and Lewis came back as a sort of consultant and Hathaway felt he was being judged as not up to the job.
From having been a sort of saintly person he did turn a bit nasty (the later episodes where he was a real shit to his sister who had been left to look after their father).
And up thread someone said about was he every romantically involved. I am sure there was an episode when some femme fatal (spelling?) nearly seduced him, very much like Morse poor upper class twit taken in by women whilst nice working class Lewis manages to have straight forward relationships with wife and daughter. Any way this woman took him back to her flat and then set it on fire or something? And Lewis rescued him? Or maybe that was a totally different detective series.
The only nice thing (or it may have been a bit aren't I virtuous) that Hathaway did was when he somehow worker out that a man arrested for a totally different crime, was probably the hit and run driver that killed Lewis' wife.
I watched much more Lewis than I did Morse, because I thought Morse was such pompous shit! And I felt sorry for Lewis having to put up with his sneering snobbery and paying for the beer!