2001 A6 4.2 - Timing chain tensioner cracked and chain jumped
 

2001 Audi A6 4.2 (72k miles) had the timing chain jump after the plastic tensioner cracked, resulting in one half of the engine shutting down.

Mechanic feels that repairing the tensioner may only fix one part of the issue, as he's not sure what other damage may have occurred in the engine. (Plastic from the tensioner was found in the oil pan). Doesn't think that it's worth the money to replace the engine with a rebuilt one. Any thoughts?

Crazy talk. Pull the pan and clean out the debris. Replace any bent valves (not sure what "one half of the engine shutting down" means") and the tensioner. If your mechanic is afraid of valves, I have a head with the cam chain adjuster in it for sale. $250 plus shipping.

Consider doing a timing belt service at the same time if the service is due soon.

If you decide to bail out and sell the car as is, I'm interested. Been looking at 4.2's lately.

Good luck!

My Q5 is 120K miles and it just had that rough idle issue today. Took it to the dealer and it's the timing chain broken caused the engine damage. Dealer quoted me $13K for redoing the engine. Am I out of luck since I'm >100K mile?

I think you're out of luck since you are on the wrong forum.
Your problem isn't uncommon. Good luck.