It depends on the circumstances of the civilization. An industrial revolution isn't something that happens automatically after a certain length of time; it depends on the needs and circumstances of the society at that particular point. The technological level of Western Europe at the time the Industrial Revolution began had been reached by China over seven centuries earlier. But China had no need for a revolutionary change in its way of doing things. It was already the most prosperous and powerful nation in the world, and all its needs were met internally, so it had no incentive for radical progress. By contrast, Western Europe was relatively impoverished and less able to support its population, so it was more motivated to seek out the riches of Asia as well as seeking overseas farmland it could colonize, and that drove advances in transportation technology such as the steam engine. And the need to compete with China's textile and ceramic industries drove the development of the factory system. And all this was made possible by the ample coal deposits that were available in England and Europe. And a society without a rigid class division between the people with the capital and the people who did the labor and tool-building also made innovation more feasible than in more stratified societies. (Although here the comparison is more with Ionian Greece, which was practically at a pre-industrial level 2000 years ago and might've had an industrial revolution if the social circumstances hadn't stifled pragmatic science.)
So it took a combination of factors to spark an industrial revolution: the right location, the right resources, the right social structure, the right economic incentives. So it wasn't just about being able to make the breakthrough, but having the need to make it, the motivation to change. Technological evolution, like biological evolution, follows a pattern of punctuated equilibrium: rather than advancing at a constant rate, it stays fairly level most of the time, but goes into a state of rapid innovation when circumstances compel the development of new adaptations. After all, if you're already adapted to your environment, if your way of living meets all your needs, there's no motivation to change. It's only when there's some mismatch between your lifestyle and your needs that the incentive to innovate arises.
This is hard for us to see because we've lived all our lives in a time of constant and rapid progress. But over the grand sweep of human history and prehistory, that's the exception to the rule. Greece could've industrialized two millennia ago, but they didn't have the social foundations for it. China could've industrialized nearly one millennium ago, but they didn't have the need for sudden, rapid progress.
So there's nothing implausible about a fantasy world's society remaining at a fairly steady level or progressing only slowly for thousands of years. Indeed, magic would probably fulfill many of the needs that higher technology meets, rendering it unnecessary for the society to develop higher technology.
But Professor Zoom makes an excellent point. There are many determiners of progress. Even without an incentive for rapid technological development, there are still changes and innovations in abstract knowledge, practical techniques, economics, art and literature, social dynamics, and so forth. A culture is a living, changing thing. So for a society to remain exactly the same in every respect for thousands of years is totally unbelievable.
