A timing chain should easily last the lifetime of the engine or even the car or vehicle.
That is as long as you constantly keep up on the oil changes as in changing the engine oil and oil filter every 3,000 to 6,000 miles.
The timing chain may stretch overtime though which could then lead to your engines timing being off but that usually doesn't happen until around 300,000 to 400,000 miles or more.
I have the original timing chain my a truck that has 500,000 miles on it and I've always changed the engine oil and oil filter.
I plan to rebuild the motor eventually and then the timing chain will get replaced then but for now it's okay.
However anything can happen and it is possibly but very unlikely that a timing chain could break which would then leave you stranded.
But if you want to replace the timing chain after 150,000 to 200,000 miles just to prevent problems then that is okay too.
The timing chain and gear set can cost as low as $20.00 to $50.00 but it is a job to get to the timing chain and replace it and you need to seal the timing chain cover up and make sure the marks on the gears are aligned correctly otherwise the timing will be off and your engine will either not run at all or run really rough.
Having a good auto shop replace the timing chain can cost around $200.00 to $500.00 depending on how hard it is to change your timing chain.