Sounds like the Optical light came off the PCB (Printed Chip on Board) from my research this is an ongoing issue with the mouse after being dropped.
-My best bet would be that the light came off the solder joints with - or + connections and causing it not to light and unable to reflect a light to the sensor.
You could try taking the mouse apart by locating all the screws, some may be under the mouse glider pads on bottom of mouse, and pop it open with a spudger prying tool.
Make sure both the LED connectors are seated correctly into the solder joints on
- and + on the PCB.