If it were my camera, I would have it repaired. I would suspect that the repair shop would replace the lever. While you could bend it back yourself, if you bend it too far, you could damage the stop down levers on every lens that you mount on the camera. That alone is reason enough to have it done by a Pro.
As for your 400mm VR, it should be razor sharp wide open, so a bent stop down lever should not make much of a difference, though a bent or warped mount will. Good Luck and Enjoy your Nikons!