2013 A5 with 64k miles. Bought 2.5 yrs ago, used. No issues in last 2.5 years. All maintenance kept up with; engine oil, filer, air filter, fluid checks, etc

Last week, started running rough. Engine was missing. Trouble code 303 for misfire in cylinder 3. Replaced all plugs and the #3 ignition coil. No luck.

Dealership tested and found low compression in cylinder 3. Did my own research and found its most likely valves or piston rings.

Audi suggested engine replacement @$14k. lol. yeah

Talked to mechanic friend of mine. Explained everything, including the detail that i noticed engine burning oil when i started after changing plugs and ignition coil. They thought piston rings. Cheapest way out was to replace the engine.

Filed a complaint to Audi. A modern engine should last longer than 64K. I plan on going and raising some hell in the dealership.

Here are my questions:
1. Chances they cover the engine at no cost?
2. How difficult to replace engine? I have done a ton of maintenance on other vehicles, including transmission replacement. Not really that experienced with Audis
3. Any DIY guides on an A5 engine replacement?