When a throw out bearing on a manual transmission goes out there will usually be a warning sound such as loud grinding or squealing when you depress the clutch pedal.
So if you hear that noise then it's usually a sure sign that the throw out bearing is about to go out or has gone bad.
If you don't get the throw out bearing fixed when it starts to fail it could lead to other problems such as destroying the clutch pressure plate, and clutch disk and maybe even damage the bell housing of the transmission depending on how your clutch works.