It’s better safe than sorry
Worn bearings, if left long enough, can do serious damage both to your hub and your health. Left to rattle around, a worn bearing can scallop out a larger recess in your hub meaning that standard-sized replacement bearings will no longer fit and a new hub is the only proper way to remedy it. That doesn’t stop those inventive bodgers, though, who’ll no doubt find a way to make the bearing fit using a homemade shim fashioned from a Coke can or a liberal application of loctite.
But worn bearings are no joke, and as they’re so simple to check there really is no excuse for allowing them to degrade so badly that they pose a safety risk. Just raise your bike’s wheels off the ground and then try to move them side to side. Any lateral play is indicative of excessive wear and it’s time to fit a new set of bearings.