If you never cut your engine off what would probably be the first thing under the hood to fail?
i don't know
Can anyone answer this?
Like Tom said, if the engine is in good working order it will run out of fuel before anything fails. If in a weird situation where you kept fuel in, as in an experiment, very unpredictable. Matter of fact impossible to predict. Manufacturers run cars on test-tracks 24/7 for days, just to find out the answer to your question and different things eventually fail, depending on car. At idle...who knows?