pylon:
That device is visible for about 1 second, maybe two. Did you really check the device manage in that time frame? As I wrote: you want get the correct timing in the first try but most people had success with this method.
If you don't have the time to try, get an ICSP programmer and burn a new bootloader to the Leonardo.
Nope, it isn't visible. I checked it several times, plug-in and unplug and looking at the device manager. There is no "serial" device detected. Not even for a millisecond.
So it seems that the only way to get the arduino back working, is programming it via an external programmer. I have to admit that I was a little bit suprised, that there is no way to just reset the arduino back to "factory settings".