The serpentine belt on a vehicle lasts quite a long time so it's not a belt that needs replaced that often.
Most serpentine belts can go as long as 60,000 to 100,000 miles and sometimes longer but you should inspect the serpentine belt after every 5 years or so and look for cracks and check to see if the rubber of the serpentine belt is drying out.
If you notice any cracks or notice the serpentine belt coming apart then it's likely time to replace the serpentine belt before you're stranded.
My serpentine belts get replaced every 5 years as preventative maintenance to prevent a breakdown and I replace the serpentine belt always before a long trip if it's been almost 5 years or 5 years and then I keep the old belt that is still okay with me as a spare part just in case something happens to my new belt.
But as long as you're replacing your serpentine belt every 60,000 to 100,000 miles then you should be okay.
A common symptom of a failing serpentine belt on a vehicle is a squealing noise when the engine is running or when you accelerate.
A Squealing noise from the front of the vehicle is a sign usually that the serpentine belt is going bad and should be replaced.
If the serpentine belt breaks then your power steering and other engine stuff such as alternator, water pump etc will stop working and you'll be stranded.