Timing chains rarely fail and usually last the lifetime of the car or vehicle or the lifetime of the engine as long as you keep up with regular oil changes and proper maintenance of the engine.
However sometimes the timing chain may decide to fail anyway but usually the timing chains last well over 200,000 miles before needing replaced.
If your timing chain does fail the symptoms of a bad or failing timing chain include engine misfiring, metal shavings in your engine oil, engine rattling.
Your engine may be hard to start or running rough even after doing an ignition system tuneup.
The timing chain is important to your engines timing and when it fails completely you'll not be able to start your vehicle back up.