Welp, this sucks. My controller is no longer recognized as a USB device by any of my systems (10.10 and 10.11). So, I'm forced to conclude that it's dead.
This is pretty disappointing because I haven't used it that much. It's probably only had 10-15 hours of use, and it's been stored in a reasonable place (my home office where basically all of my electronics live).
Maybe I just got unlucky?