Think of the alternator as a rectifer and motor combo used in reverse...spin the motor and the output terminals feed electicity (technology is moving a wire loop in magnetic field it will generate electricity, only many more loops and spinning it at a fairly high rate of speed).
So your real question is what can go wrong...even though it is a very reliable system: in a high heat, high vibration harsh environ 1) the magnets may become unseated, or degrade magnetic properties. Bearings can lose lubrication, causing runout and excessive wear on the bushings or laminate armature or windings may get scuffed on magnetic pole pieces, short out against the metal bits spinning around at 4,000 RPM. Or if something overheats windings, carbonizing insulation, short out to case and burn out the regulator, and cascade into catastrophic failure.