Gary Johnson wanted to keep Ryan Law. It was Argyle that triggered the return. His opportunities might have been reduced following Dean Moxey's return to fitness, but I suspect that Johnson would have tried to accommodate both. Moxey is a versatile player and can play in a number of positions as well as left-back.
Ryan Law is more naturally a left-back in a back four, whereas Adam Lewis is more naturally a left-wing-back in a 3-5-2 (or similar) format. It will be interesting to see how Ryan Lowe plays this one in the coming matches.