A timing chain on an engine controls the engines timing so that it fires the cylinders correctly and at the proper time.
If the timing chain were to break on you then your engine would stall out and then you'd possibly get metal shavings into the oil.
You will usually hear a slapping noise in the engine if you have a timing chain that is coming lose and about to break.
Your engine may start misfiring and be hard to start or stall and then when and if the timing chain actually breaks on you then the engine will stall out and not run anymore until the timing chain is replaced.
Without a timing chain your vehicles engine will not start or run.
Typically timing chains in properly maintained engines will last the life of the engine or vehicle and can last from 200,000 to 500,000 miles before needing replaced.
But for timing belts they typically only last around 100,000 to 150,000 miles before needing replaced.
But timing chains are made of steel and are very hard to wear out but they can break.