Stepper motors generally are really robust, they run for years at high temperatures with little change in their characteristics. I have a dozen or so Nema 23 and Nema 34 steppers here that are getting on for 30 or more years old and they work just the same as they did on day one. The biggest killer is people trying to mend them, once dismantled they wll never work again as they are magnetised in their assembled state and once the two halves are separated the magnetism goes out of the window.

The trouble is that the recent increase in all things computer has led to massive sales of low end, home user CNC type things and prices falling so I reckon something has to suffer and generally it is quality. I would not immediately think a stepper was failing, it would generally be at the bottom of the list after all else has been proven to be OK.