And replacing him by which player ? There isn't any RB at his level on the market so not a good idea IMO.
I think they keep him for another year to please Neymar, but if you look at his performances as well as stats he is declining. If it wasn't for Neymar, I'd say sell him now while we still have the chance to get some nice cash for him. I'd say about 23-26 million euros is a good amount for a RB player with 135 assists in 460 matches. One of the best I've ever seen, but we won't see him at his prime again...
And replacing him by which player ? There isn't any RB at his level on the market so not a good idea IMO.