It does appear that Barry decides whether he stays on the park or not. It was clear both at Motherwell on Wednesday night and at Ibrox yesterday that Ferguson was running on empty after an hour, and for the good of the team he should have been substituted and replaced by Edu.
Now I've now doubt that Barry believes that he has Rangers' best interests at heart, and being the captain feels he is best served being on the park. It takes a strong manager to over-rule that, and so far Walter has admitted that Barry told him on Wednesday that he wanted to stay on. That cost Rangers two points, in my opinion, because we did nothing in the final half-hour of any threat, having dominated the first half when Ferguson was playing particularly well.
Yesterday was interesting. I was watching Mendes and Ferguson very closely to see if Fergie would have the "ma baw" attitude with Mendes the way he did last season. To be fair he didn't, he let Mendes drop deep and pick up the ball on occasions and didn't demand the ball off him for no apparent reason. Ferguson and Mendes were swapping positions regularly, taking it in turns to push on while the other held behind, and it seemed to work quite well until Ferguson tired.
As you said, TGO, the time to judge is when Ferguson is fully match fit, which he appears to be far from at the moment. He started very well yesterday again and faded badly.