View attachment 64681 This was dragging on my daughters car today. I can't see why it needs to be reinstalled.
My guess would be a heat shield. If the car is never parked over a pile of dry leaves or pine needles.......then you might not need it. If it IS parked over something combustible sometime, you might be VERY SORRY if it is not still in place. A car on fire is not a pretty thing.
"Plastics" can be designed to do all sorts of things. So.....what is behind that plastic flap ? Or above it, depending on your perspective ?? If it is any part of the exhaust system, I definitely would replace it. Can't be THAT expensive; it's just "flimsy plastic" right ?? It might be interesting to have a dealer's parts guy look it up and see what it is CALLED.