Differential thrust with one inoperative thrust reverser isn't a big deal. It's something to be aware of but not something to be afraid of.
It helps if you let the auto brakes do their thing and not disconnect too early; then all you have to do is steer with your feet: heels on the ground. Considering the length of the runway, and the need for 180, there should not be any need to disconnect the AB's. I'm not understanding the thoughts about mis-selecting TOGA, or flaps up knocking the Rt. TL to forward thrust, or some other curious 'what ifs'. They were so far down the runway, and judging by the tip over the edge, they must have been going quite slowly and just nudged over the edge, otherwise they were swimming. The skid marks from the mains suggest some heavy stopping forces. As has been said, the investigators have all the info they could wish for and must surely have the answers. When will they tell the rest of us is the question.