So if no communication, challenge and response by 100kts:
In A340-600 at 380 tons, the F/O will take control and stop by 100kts. The problem getting airborne and flying it around again and dumping 115 tons. MLW 265 tons The complications gather at a rapid rate of knots once airborne and even then, the incapacitated pilots needs urgent medical attention.
However, at 380 tons, there would be a double crew (leg distance is ULR), but the other captain from crew B, sitting in first observers seat, (an Airbus term) is not at the controls and I am sure he would also tell the F/O to stop by 100 kts. Autobrake is working so don't touch the brake, unless autobrake is not working. Reverse thrust is not considered for rejected take-off anyway, incase the engine had failed and was the reason for the rejection. The F/O is welcome to use what he needs and what he has at his diposal, but thrust reducton is a must, in line with directional control.
The rest will be history and remember "PARK BRAKE SET", otherwise nothing like doing 15 kts in cirlces while you're trying to pay attention to other things in the cockpit. Work load has to be at it's highest form on this one, for a single crew.