Take it to an independent to get a price for a new timing chain fitted, along with rollers, tensioners, etc. You'll find that the price will probably be massively less.

As to if you don't get the job done ? It could last 2 days, or 2 years. When/if it does fail, the car will be scrap.

Timing chain failure will be terminal and mostly likely require a new engine. Fine an indy and get fixed at half the cost or sell the car.

I don't really follow the logic that if a repair costs more than the car it's not worthing doing.

Logic for me would take into account the cost to change to a new car that I wanted.

So if a new car was £5000 and the old car is worth £1000 and the repair is £1300 for me it would £4000 for a new car or £1300 to repair the car i have. So a repair saves me £2700

The alternative of buying anorther car for £1000 - £1300 makes no sense as you have no idea of issues the new £1000 car will have and how well it's been looked after etc