Alves should be sold but it is not because he isn't good enough for the club anymore. He should be sold because this could be the club's last chance to get a decent amount of cash for him.
Ever since Abidal left, the defense lost balance. The club can buy as many world-class center backs as they want, and although it would certainly improve the current defense, they are still going to get exposed when we play both Alba and Alves at the same time. Under Guardiola, granted we didn't have the best defense in the world, but they also didn't get the credit they deserved either. I'm fairly certain Barca broke a few clean-sheet records under Guardiola and I think part of the reason for that is that the defense had more balance with Abidal. Abidal could handle himself offensively but he was twice the defender both Alba and Alves are now --- he was also a beast, which helped.
Obviously the club isn't going sell Alba since they just bought him, he's young and he's from La Masia so the logical course is to sell Alves and hopefuly replace him with a more defensive minded full back who can also offer something offensively (2 centerbacks are also needed of course). Ivanovic would be perfect fit IMO but no chance Chelsea (Mourinho) would sell to Barca.