Yep, most likely toast time. Interestingly if you had placed +7.4 vdc onto the reset pin then nothing bad would have happened as the reset pin has no positive voltage clamping diode as that is how you enter HV programming mode, by placing +12vdc onto the reset pin. I guess your 50/50 coil toss came up tails and you lost. 
Now as to the limit of the damage, it could be limited to just the 328p chip as the damage may have been limited to the chip via the negative clamping diode. If the PC still recognises the initial USB connection when you plug the board into the PC, run the loop back test and if results are good a simple $6 chip replacement may get you going again.
Lefty