It's a reasonable thought to sell Pjanic and use the money from his sale on a B2B player which we currently lack. I think Bentancur's future is in Pjanic's position. His long passing is not on Pjanic's level but in the more traditional categories for the position, he is doing well (height, speed, tackling, anticipation). If we can shift the emphasis of play from the regista to something more in attack, I think Bentancur will be fine there.
He can't pass out of a press like Pjanic but he can dribble, so that's a bit of a trade-off (although Pjanic has gotten a bit sloppy when pressed lately).