I taught for two years in a school that fitted every definition of coasting. Most staff had been there more than 10 years and a few for more than 30 years.
The work was relatively undemanding, results were average, the staffroom veterans had the children well under control and there was a good social scene.
I could have settled for the quiet life as, indeed, had many of my colleagues. Unluckily for them, however, soon after I left there was a major reorganisation and the school closed.
There were early retirements, redeployments and, sadly, some stress-related illnesses.
What is the right thing to do?
When you feel it's time to go, get on with it. There really is no comfort zone. If you don't look ahead with a view to controlling your working environment, it will change around you in ways you can't control, probably quicker than you think.