Yeah, trying with a Pololu programmer:
$ avrdude -p m2560 -c avrisp2 -P /dev/tty.usbmodem00143251 -U flash:w:Arduino-COMBINED-dfu-usbserial-atmega16u2-Mega2560-Rev3.hex.txt
avrdude: stk500v2_command(): command failed
avrdude: initialization failed, rc=-1
Double check connections and try again, or use -F to override
this check.
avrdude done. Thank you.
Board seems to be toast.