I was wondering if anyone had a clue on how long a timing belt has lasted before it broke

and how can I check if I need a replacement ( not counting the milage)

A6 quattro 2.8 L 2001




I posted it before, but it doesnt appear ont the page links

 

You can take the accessory belt off and then remove the front cover to expose the TB. The TB should have no signs of unusual wear, shouldn't have any cracks, stripped teeth, or unraveling fibers. Moreover, the rubber should be still "pliable" and not stiff/dry/brittle.

Here's the 2001 A6 Maintenance Schedule, or here - if you like the .pdf format.

 

It is not just the timing belt you need to worry about. The t-belt goes around a tensioner whose bearing can fail while the belt is perfectly fine (ask me how I know!). The water pump is also driven by the t-belt and its bearings and/or seals can fail. All I can say is don't push it much past the recommended interval or one day you will have a very unpleasant surprise.