Running an alternator till it fails to produce electricity is usually a voltage regulator failure. Voltage regulators generally don't make any perceptable sound, but if you have problems your voltage will fluctuate, and one day it just won't work.
Yes, alternators are serviceable, and you can get bearings and even new voltage regulators for them, but if all you want is a stock alternator you can usually get a rebuilt stock GM alternator with a lifetime warranty for $50. I did splurge when I put a new alternator in The Beast - When the original alternator gave out I put an upgraded 165 amp alternator in. The Buick and Rusty are both running 105 amp alternators when they came stock with 70 amp alternators. I always believe in oversizing the alternator.
If you're running an oversized alternator you won't get a $50 one. The last alternators I bought were oversized, but still stock alternators in my Buick and in my 86 Chevy. I think those ran me like $70/ea and came with a lifetime warranty. I think I bought them at the local NAPA dealer. I could have had the original 70 amp alternator for about $50. The alternator in my 98 GMC is a custom aftermarket alternator, 165 amp. If I remember correctly stock is 120 amp. I oversized the alternator because its nice to be able to jump start anything, and I was thinking about installing an AC inverter on the truck at the time.