If the alternator fails (usually open circuit) or a brush fails (open circuit) you won't immediately lose your lights, though they will begin to dim. The "GEN" idiot light on the dash panel should light up. You can put a multimeter on your battery to check the voltage when the engine is revving around 3500 RPM or so - it should be around 13.5V if your alternator, brushes, and diode board are working.
If it is a high pitched squeal, it could be that your timing chain tensioner is worn out and/or broken.