2005 FX45 Issues

I know this is not supported, so just want to post the problem and see what smarter minds here can figure out.

About 6 weeks ago, driving on the highway, an exhaust pipe broke off and I had to drive about 50 miles home pulling my boat. Since getting it repaired, the car has no power, this is only after it's warmed up.

It drives perfectly normal for about two minutes.

No engine light ever in 14 years.

Took it to the dealer and asked them to check it out. They come back with:
FOUND KNOCK SENSOR CODE IN ECM. LOTS OF LEAVES AND TWIGS IN MIDDLE OF ENGINE WHERE KNOCK SENSORS ARE. NEED TO RE AND RE INTAKE MANIFOLD AND CHECK KNOCK SENSORS AND WIRING. POSSIBLE WIRES CHEWED OFF AND IF WIRES OK MAY NEED TO REPLACE KNOCK SENSORS.

That's a lot of maybes in there.

Would there be a code in the ECM without the engine light coming on?
I'm suspect because they said if they didn't find anything, there would be no charge for the diagnostic, making them want to report something. Especially when they tell you $1430.00 for two knock sensors, not including any wiring. No guarantee that it will fix the problem.

If a wire is broken, would the PCM pull timing when it goes into closed loop?
Did this wire break off, exactly when the exhaust pipe broke apart? Coincidence?

Any ideas before I have to pull the intake just to investigate?