I am not sure anybody has really nailed down the left wing slot, especially considering Martinez likes one flying winger and then one more creative clever player (operating from the left).
Likewise Barry's game time will increasingly need to be managed, but he is a very important player for us. I could easily see a rotation with Baines? Who knows. I think all I will say though is Martinez is quite good at utilising his squad and being inventive with different roles for players. I would like to see Baines stay and it would be good if his workload was reduced.
I know some fans like to see players once they turn a certain age bombed out, it's far more sensible to reduce game load. They still have a lot to offer.