they can last for decades, most of these movements aren't rocket science, at this point the movements are pretty much identical to the originals(that's because the patents expired so they can be copied). Granted there is a lower barrier for quality, so it might break after the first couple of winds...but if it survives the first few winds, chances are it'll be fine for a long time...unless you do something to mess it up(i.e. you decide to go play sports while wearing one)
here is the thing, even if the replica shits the bed after 5 years, it'll still be cheaper to buy a brand new one(which after 5 years will be even closer to gen) than it would to pay to service a gen. Or you can just buy a brand new rep movement for peanuts and swap it in.