Yeah pulling the plenum was completely unnecessary. Schedule that DET sensor replacement job for when you do a timing belt next. The DET sensor itself is fairly resilient... unless of course it's a puddle of melted plastic from an overheating event (that shit will never work again). Pretty sure there is a resistance test from the sensor side pigtail lead that is at the rear of the engine. Yes, knocking is bad, BUT if you are sensible with boost and tune it should not be a problem. And even then if you do go wild it's outside the capability of the stock ECU in many cases, so you could look at other methods of knock detection.