I had one popped out when I hit a piece of tire on the freeway. I told my service advisor that that thing just popped put. I did not tell him about the tire.

Yep, the black bezel surrounding the sensor is gone, but the sensor itself where inside the bumper and still connected and beeping as it senses the ground.
Dealer said sensor is around $125 , not sure about the labor, but they fixed it in less than 30 minutes. My extended warranty covers it as bumper to bumper. I had to pay $50 for deductible. I made a mistake paying deductable, since I could have also point out some more warranty stuff like my broken cup holder.
The $50 deductible warranty bumper to bumper is actually per visit and unlimited warranty work per visit.