Reversed Input Voltage Arduino Mega timeout communication with programmer error On the barrel connector I accidentally reversed the input voltage to an Arduino Mega. The center post received ground while the outer connection received +12DVC, basically I have the Arduino -12VDC. I have since fixed this problem. When I power the Arduino with the USB I am able to program the Arduino without a problem. When I power the Arduino with the +12VDC the program still runs (confirmed by programming the blink sketch). If I have the +12VDC connected and try to program the Arduino then I get the timeout communication error.

Do I just need to re-burn the bootloader? The Arduino's symptoms match those listed here when both cables are connected: Arduino Mega timeout communication with programmer error

Is there anything else I should verify? Or is the Arduino always going to be damaged?

Also as a note I did the same thing to an Arduino Uno (same rail going to both) and the Uno has no problems when both USB and power are connected.
Chances are you have blown up the circuitry that performs the switching between barrel jack and USB power sources.  As a result the USB interface chip isn't getting power when it should.

In short: "It's dead, Jim!"